Then they can go to the computer! Evelyn keeps track of her finances using a computer program, it's better than doing it on paper. She breaks it up into categories: housing, food and household, transport, healthcare, activities and leisure, gifts, and Surprise Large Expenses.
Housing is a much lower chunk than it used to be when she was paying the bank back for the house loan, which is nice! Her property taxes come to about $1200 a year; she gets a bill four times a year, but sets aside $100 per month so she'll always have enough to pay the bill without dipping into savings. She also gets bills for electricity, gas for heating, water use, the television, and the internet, and the truck that comes to pick up her trash and recycling; she's not unnecessarily wasteful, but she does inevitably use a lot of hot water and the dishwasher and laundry machines both see heavy usage. She budgets $300 a month for it, though it's usually a bit less. The house also needs repairs – not in any given month, necessarily, but it's an older house and she wants to have money set aside if the hot water tank or the furnace or the oven or the fridge or the sump pump that keeps water out of the basement break and need to be repaired or replaced. She puts down $50/month for house maintenance, which comes to $600 a year; sometimes she has a lucky year and only needs a handful of inexpensive repairs, but a new furnace costs thousands. So that's $450 a month on having a place to live - which is actually pretty cheap! You would have a hard time renting a one-bedroom apartment for that little if you wanted to live downtown. Owning a house is a good deal once you've paid off the mortgage.
Food! Evelyn does put some effort into minimizing grocery expenses – not to the extent of not buying meat or produce, she can afford it and a varied diet with lots of protein is important for growing kids, but she shops in bulk which is cheaper per-meal when she can, and does a lot of home cooking, and buys vegetables in-season when they're cheaper, and only buys frozen prepared meals when they're on sale. Her grocery bill also varies a lot by who's living with her, obviously, when it's just her and one kid they spend less. She budgets $100 baseline per person per month, so $400 for this month; smaller kids do eat less than an adult in total, but they also tend to be pickier. Non-food household expenses are things like hand soap and shampoo and cleaning supplies and toilet paper and kleenex. That varies less based on how many kids are around, though the reason she decants toiletries into little containers is because otherwise a lot of kids will waste them. She budgets $100 a month, though also she buys products in large quantities when they're on sale, so it's variable month to month and she averages it. $500 a month on food and household supplies, then.
Transport means gas and car insurance and repairs. She spends around $125 a month on gas. She has to have her car insured - that means that if it gets damaged in a crash, the insurance will pay for it, and it's also legally required to be insured in order to drive - and that's once a year but costs $900, so she sets aside $75 a month for it. She sets aside $50 a month for car repairs and cleaning. (It's mostly cleaning; she has kids in her car and often they make messes.) $250 on transport.
Healthcare in the form of doctor's appointments is mostly covered by insurance - which she doesn't even have to pay for, for her foster kids, and Social Services reimburses her for doctor's office copays – but insurance doesn't cover over-the-counter drugs or, like, bandaids. She sets aside $25 per child per month. (Sometimes non-insured health care costs a lot more than that, but foster carers are paid more to look after 'medically fragile' children). She also has to pay $400 a year for her own health insurance; it's technically through her employer, which is the fostering agency, but they don't actually pay for the premiums. She allocates $50 a month for Evelyn Doesn't Get Sick. (If she has large healthcare expenses, which she might well at some point, that has to come out of savings.) $125 this month on healthcare.
(Clothing is another essential but the government provides money for that specifically for her foster kids, and Evelyn herself kind of just...doesn't buy new clothes very often, right now, and it's not part of her core budget. Children need clothes a lot more often because they're growing and more active.)
So, yeah, those are more or less the essential expenses for maintaining their household. A little over $1300 a month. If Evelyn only had Iomedae and Alfirin at the standard emergency foster care rate, she would be getting about $1400 a month and her expenses would only be a tiny bit lower on groceries etc. In practice, of course, sometimes she has one kid in a given month, and sometimes she has three kids who are all high-needs. She also gets paid to run trainings for other foster parents, but that's less favorable for tax purposes. (Foster care payments aren't taxable, thankfully, and Evelyn qualifies for several tax breaks.)
Anyway, with three kids and Lily getting the foster care payment rate for a specialized placement, she's earning $2600 for this month. Her best guess is that next month, once Iomedae and Alfirin are more formally assessed, they'll both qualify for an additional $150 a month special rate and she'll be earning $2900. On average over the whole year, she probably makes about $2500/month in foster care support payments, and most years she'll make another $5000 - in good years, another $10,000 post-tax - on teaching other foster parents, which she puts directly into her personal retirement savings.
She has a rule that she tries not to spend more than $2000 a month routinely; if she earns more in a given month, it goes into her easily-accessible savings to cover periods later when she's earning less, and so that she'll have a cushion for large occasional expenses like a new car. (Going into debt to buy a new car, unlike going into debt to buy a house, is something Evelyn's mother taught her was a bad financial decision, but also you absolutely cannot live car-less in a suburb in Reno). As a very approximate rule of thumb for when it's the middle of the month and she hasn't added up expenses yet, she's happily willing to spend up to $50 per kid per month on Nice Things (material possessions) and $50 per kid per month on Nice Things (activities and leisure), plus their routine allowance which comes to $40 a month. The start of a new placement also isn't 'routinely' and she's willing to spend a bit more when a kid just arrived with none of their own possessions; she would have bought Iomedae a $250 bike without a second thought, and it's more or less sustainable for her to do that with all her foster kids. A $450 bike is...well, it's not actually a problem, she's probably still earning more this month than she's spending, but it's not something she could casually do for every kid.