Hi Elle,
Your concern is common it seems but does require a certain level of what is called a "leap of faith."
My advice to you is this;
Get a budget, stick to your budget, live by your budget and so on.... Your budget should include all the "other" things that comes along with riding, gear, tires, oil and such. You are not ready until you have your bottom line safety budget in hand. Whether paid in cash or via financed. Your call. At the very least take a veteran rider with you to make sure you don't get a money pit for your first bike to bring it up to your standards of safety.
Next... be a savvy shopper, there should be some good 250's and maybe even a 300 within the <2k price range that are ready to roll. It is a sellers market right now so just accept that you will pay a bit more for a ready to ride bike.
Also, don't buy the first bike you test ride. You never know what you like until you try. While I don't say the bike picks the rider, I also don't say the rider picks the bike. You like what you like while window shopping, the agreement that you AND the bike come to while together is what is important. AKA bringing a smile to your face.
Let's give you your first riding lesson. Aka, how to check your tires. There are wear marks on tires. There are date markings on tires. Neither can be hidden. For your first bike, the wear bars on the tires should have a good amount of tread above the wear bar and the date should be well within 5yrs of age with no signs of cracking or anything else. That little bit of knowledge will save you $200 in tires/mounting.
Also, have you given any thought to the BRC or MSF course in your area? You have to sign up early to get a spot as they fill up fast and you're LATE. You don't even need a bike to learn to ride. If you haven't got a spot, call NOW!
Welcome to riding, there is alot to learn, it's a lifestyle, not a whim hobby and patience is key.
Good luck, happy riding and keep us in the know.