I dont have ant treadmill recomendations for you.. but,
I was given a treadmill that another family member spent 600$ on about 3-4 years ago and never used.. It was 600$ and it is pretty shitty, nothing compared to the gym.. I opt to run outside at parks, schools, or the treadmill at the gym, instead of running on it.. Im 6'3" 220 and I may be too big for it.. also make sure you are going to use it..
Either way, dont buy your treadmill on the web, make sure its a good fit and sturdy enough to put up to your abuse, 500$ is a lot of money..
Dawookie