Sorry dude but you were ripped off. $8000 is a fairer price for a 4Runner w/ 150k miles.
I bet it is all original as well. You will easily have $3000 is maintenance by the time you hit 225k miles, assuming you take it somewhere for the work.
OP, those low miles are good but the price is still pretty high.
I picked my 2001 limited last February with 150,000 miles on it and paid 11,200....So ya, I think its a good price.