This is car really just a collection of car parts and potential work:
Offer him $4,500 for the car (Engine $1,500 + Body $1,500 + interior 1,000.+ suspension and glass $500 = $4,500)
Cost:
Trans rebuild - AAMCO $1,100 maybe less if just a bunch of seals and gaskets
Brake Rebuild all 4 wheels including wheel cylinders and master cylinder - PEP Bpys/Mienke $800- 1,100
Axle(s) - Replace $500 - $600

If you get it take it to more than one mechanic for estimates