The mods here should be helping you out by posting this where it belongs...
But to answer your question, he is asking way to much for something you will end up spending "a lot" to get in top condition. The stalling has nothing to do with the exhaust leak.
If you were to take this to a shop, you are looking at a couple thousand at least to get it to the condition that matches the asking price. 60k tuneup alone is going to run you about $800 - $1100. Depending on what's going on with the brakes, $200 - $600. The question should be asked "why is the down pipe in such poor condition?". Add another couple hundred for the down pipe, plus install, and $500 or so for the struts installed... All drive train fluids should be changed.
All that is just from what you have explained. The stalling out could cost much more at a shop to figure out if it's not obvious to find.
My advise is to take it and pay $75-$150 to a shop to give it a shake down. Then negotiate the price after you are educated on what it will take to get it running/driving. If he does not agree to this... WALK AWAY!
In that condition IMO it's worth about 6k