Ive been looking for an 8.5 rear for my car and came across a guy with 2. One non posi for $550 and a posi for $800. Are these reasonable prices? How much would it cost to convert the non posi to posi? I was originally going to get the posi, but could also buy the entire non posi car for $1200. The body is shot but has non posi rear end, hood, trunk, decent interior, motor(hot air) and trans