That... is not the tavern corridor.

Like, it's definitely a tavern! Full marks, Night realm, for generating a tavern.

No points for the... exploding stars?

Well, sulking in her room is not going to actually help. She steps through into the Mystery Tavern, and looks around to see if there are any other obvious inhabitants.

There are, actually! It's not very crowded, so there are only about a dozen or so folks in the room. Mostly humans. Nobody else seems to be alone, though; everyone's seated at a booth or table with at least one other person. About half of the people inside are wearing floppy red hats with white trim.

Oh great, commentary. Thank you very much, The Night Realm.

She'll drift around the tables as if she's looking for someone in particular, but actually listening to conversations, to attempt to orient herself on who even are any of these people.

"—so then I said, do you want the payment plan to be based on the grand total, or the total due after I apply the credit from your return? And they say, yes I want a payment plan. So I'm like, right, let me rephrase. Your grand total is eight hundred ten crowns, and you've got credit with us of a hundred twenty. You can either pay a hundred fifty now and then two payments of two hundred seventy, or you can have three payments of two hundred thirty crowns. They say they want three payments. So then I say, do you want three equal payments or do you want today's payment to be a little smaller than the ones for the next two months. Now what do you think they said after that—"

"Really?"

"Yeah, it's all in your attitude when you open the door."

"How so?"

"Well, it works best when it'd be convenient but you're not desperate. You can't be too demanding and you shouldn't beg, but you shouldn't be too casual either."

"Are you sure you're not just lucky?"

"Which one of us can get a door here on demand, again?"

"—and when he opened up the portal in the season finale? Whew! He can open my portal any time he wants."

"Would you say that if he was here right now? The door did open a minute ago…"

"One, I saw the person who came in and it wasn't him. Two, you know I would. Three, it honestly feels like such a ripoff that I've never met a fictional character in here, even one I don't carnally desire—"

So, this is a place some of these people have been before, they mostly seem like they've been here a while, and it's still pretty Leaguish in here - someone's talking about absurd sums of money, someone's talking about fancying a play character, and the other set are discussing the mechanics of the place. She circles round to listen closer to the middle group, in case they want to talk more about how it actually works; if she's starting to look suspicious, she'll take a seat nearby, get out the notebook with the fancy metallic-inked cover, and pretend to be reading something.

They've moved on a bit:

"So, do you know what's up with the Christmas decor in March?"

"Not really! I've never seen this place done up for any holidays, although I guess there might have been an alien holiday I just didn't think to pay attention to."

"Yeah, that's fair. Still, I feel a little silly…"

"Ah, c'mon, it's gotta be Christmas somewhere, right? If you hate it, I guess we can duck out and back in again, but I don't like to be cheeky like that."

Shortly after Halya sits down, a napkin with writing appears in front of her.

Welcome to Milliways, and happy holidays. May I interest you in anything? The first drink is free.

Okay, so this magic location communicates in writing. She's a bit dubious of the napkin as a writing surface, but gets out a coloured pencil from her bag and attempts to write back, in big childish letters:

what kinds of drinks are available?

It's more like December where she came from, but if they're talking about aliens they might just have a different calendar with suspiciously similar month names. Although if they're from that far away, she'd expect them not to be speaking Imperial...

Another napkin appears.

Any kind, from any place! You can speak aloud to order if you find that easier at all than writing back.

"How loud do I have to speak?" she whispers quietly. "And does that include potions, liquid ilium distillates, something that can be refined into mithril..."

As loudly as is comfortable for you, begins the napkin. I can sell any of those things for reasonable prices but only primarily nutritional potions would count as "a drink."

Practically under her breath, she mutters, "What do you consider reasonable prices?" If the first one is free it stands to reason that the next one is expensive.

It depends on many factors. At risk of oversimplifying, items that you could purchase back home will have similar prices to what you'd see from a merchant who was neither overcharging nor selling at a loss. Prices of things that aren't sold in your home world depend on other factors, since the same material can be rare in one world and common in another.