father son project

I want a cheap safe car for my son that we bring back to good condision. I'm thinking a 92-93 BMW 325 with a bad motor. Any advise on what to look for, what to avoid. I'm thinking $2000-2500 for the car if it's in very good shape but bad motor. I think I can buy a salvage yard motor for $1200, a rebuilt for $2200. What's the cost of rebuilding on my own? Remember cheap safe reliable, and son wants cool.