im looking to buy an 07 or 08 LR3 HSE or RR sport but most of them are at about 50k-80k miles. my question is, how reliable are these SUV's?

 

You're kidding, right? Seriously, you should check this forum as well as other sites for a recital of Landie issues. That being said, they really are great SUV's if you actually plan to use the vehicle as an SUV, and when they are working properly.
You might want to check Carmax on line, they seem to have a pretty good collection of lower mileage Land Rovers from time to time. Whatever you do, buy the best, longest term warranty you can find and be prepared to become well acquainted with your local LR dealer or independent repair shop.