"So, do you have as little idea what the immediate future looks like as I do?"
"That depends. I have a reasonable avenue to take if you don't want any further help from me, but if you do, it's quite possibly a better choice than my default plan."
"I would be glad to have your help if you're offering. I know approximately what the medium term plan looks like, but am completely lacking in information on questions like what kingdom to do it in and what sort of food people eat here and everything in between."
"A thousand. So you'd know better than I how much I can afford to pay you; my only reference points are curiosities and slaves."
"Start mass-producing as many devices as I know how and become absurdly rich and powerful. For a good cause."
"...How sure are you that the devices you remember knowing how to make will actually work in reality?"
"Some things can be tested more easily than others, but, does boiling water in an iron kettle still make the lid rattle? Unless that is to be a fraud as well, I can make a steam engine."
Though I can start on something smaller scale if you need proof."
"You don't have any more things from the magic to sell, do you? If that's your entire fund it's worth making sure that whatever you do first can pay for itself."
The obvious first thing to make is gunpowder. Requires very few starting resources, and useful for demonstrations if not much else. Would also be indescribably valuable for militaries, though I hesitate to hand control of the world to any country I just met."
Ah! I have it. The combine harvester. That sign said you had some familiarity with farming, though I hope it was lying; you were what, six? Anyway, it reaps, threshes, and winnows all at once. Can definitely pay for itself, or vastly improve an economy of your choice, depending on the time of year."
"I don't have especially clear memories of ten years ago but I remember weeding and raking out grain to dry and so on. It's currently early spring. Your device sounds amazing."
So the next question is, how much is what's left of the thousand actually worth? It'd be too much to hope that we're set for years, but if it's a matter of days before it runs out then I'm sorely disappointed in your economy's prices for both slaves and eccentric rich men's collector's items."
"That depends on how frugally you're willing to live and whether you're trying to support me on the amount too."
I ask because, while I'm not averse to getting an ordinary job in the meantime, it'd be a bit of a waste of time better spent on railways and telegraphs if I were rich and didn't know it."
"On eight hundred seventy-five you are not rich but you will not be out of money in a week. For maximum frugality, we can sleep in a church attic as charity cases, eat mostly rice at whatever hours the clergy aren't using their stove, and not replace your bizarre outfit. We could probably coast for a year like that if necessary, which it probably isn't. We could also rent either one or two rooms in a boarding house, try not to develop rabbit starvation, and get you normal clothes and me a pair of shoes that cover the heels, and we're probably covered for two to four months."
I could have a machine built in that time; do you think land owners would buy them before seeing the results? There are also other marketable things to start with that could go quick enough."
Other possibilities are things like communication faster than any messenger can travel, light with no need for burning, or rendering buildings immune to lightning strikes. No way to prove that last one works, though."
"Probably better to have something else propping up your reputation before you try that. The others could be extremely popular, though."