Paint ,Polish , and Replacement.Investment in parts such as hoses belts ,tires ,headlights and doors,rear lens units,replacement seat covers for front seats, window seals ,window motors(if needed),brakes,dash pad,a/c compressor ,wheels refurbished.After that cost Im guessing his out of pocket cost is $3500 & change in parts.Paint $350 if he does himself.A/C himself .Car bought for $3000 or under . Doubling his money.Time, effort and overhead ,hes about right.The motor and trans would be in question though.Trannie and motor rebuild would be over budget .Just an educated guess,my 69 Mach 1 didnt make it thru total restoration, ran out of the budget and sold it under investment. He needs to be more detailed though , no rust means no rust.