Tony Dows

Hi...I just picked up a 2002 estima and want to replace the head unit (fh-p66md) with something that has a sat nav reverse camera usb set up. Ive seen some on eBay from $100 to $500 but not sure which one is suitable and reliable....Should I go for 6.2" or 7"? I want cheap easy to use but not crap. How much do I need to spend on unit and fitting? Thanks Tony