Definitely do a PPE - the long term expense can be much greater (and disappointing) without one - even in a good price range. And definitely for an OTTB. A youngster that’s been lightly started maybe be different but with something that’s been on the track you never know what sort of things could’ve happened. Some get injured in the starting gate, during training etc even though they never actually raced.
I always do a PPE on a horse that I don’t know. The last two I bought had been with me for 4-6 months in regular work. One had just had a PPE for a buyer who backed out (no issues), the other horse I had my vet do a cursory once over. If the horse is doing what I want it to do and staying sound, I’m a lot more comfortable with not doing a full PPE with films. If it’s a horse I’ve ridden twice, absolutely I do a full exam and will at least do hocks, knees, and feet.