Congrats, a first car is a big thing! See what the mechanic says, definitely 100%, always, get the car on a lift to check out what's down under.
I just bought myself a used toyota camry, and at first was going to spend a bit more on it, but after getting it to the mechanic it turned out it needed 2k in repairs. With that estimate in hand the seller and I basically split the difference, saving me quite a bit.
As for parts, whenever dealing with a used car it will always be an issue. Especially now days, manufacturers stop making spare parts after a certain time, and price on parts that are not sold use goes way way up. Bottom line is, if someone is selling a car, there is a good reason for it. Gas mileage could also be the reason... an SUV is great until you have to fork over $50+ on every fill up.