Yes, vet care is expensive, but it's not always necessary. They do often insist on unnecessary treatments now and I think it's because most of them are no longer independently owned, they part of profiteering companies who buy multiple vet practices and force salesmanship upon the vets who work there.
Anyway: she's brand new to you so it's normal that her anxiety will be high, and upset tummies don't always require attention from a vet, there are tons of things you can do inexpensively at home. You're hyperalert right now because you just got her which is absolutely the right thing to do, but for future ref try some of these:
For upset tummies:
A great daily probiotic is Protexin Sybiotic D-C or ProPlan Fortiflora
When they need extra help, get Protexin clay, it lasts for a while even after opening
What works for mine if it goes on longer than 24 hours is missing breakfast (so essentially fasting for 24 hours, from dinner to dinner), having only a probiotic drink made with Fortiflora during the fast, and then plain rice mixed with chicken for 2-3 days and their tummies typically settle
Order all these from Amazon.
For her anxiety, she's new to you and your home so anxiety is to be expected - she doesn't yet know if she's safe. My two were both rescues, and one settled in in about 3 months, and the other was clearly still settling in up to 9 months in so sometimes it just takes a while. I got a Furbo pet cam so I can check in on them when I'm not home and feed them treats - one is still clearly mostly anxious and I could never leave him if he was an only dog, but having his best friend with him eases things somewhat.
Training treats: I used cheddar when I first got mine as a trainer recommended it as a high-value treat, but plain chicken might be best for yours right now if her tummy needs settling. Hope this helps, and be prepared to give it 3-6 months for you all to settle in together.