DIY. Yank the trans, replace the parts, plus the clutch. Maybe $300-$400 tops in parts and no worries for 2-5 years.
In a way, I'd rather get a superb quality truck that works other than a bad cutch/trans and replace it with what I know is good rather than a truck that's in "good" condition.(often the trans problem depreciates the former to far less than the "good" truck.)
Also, the 94 almost certainly had the 3.0 V6 in it, which is a no-no - avoid. Offer the guy $600 for the truck and spend another few hundred and some sweat on the fix. Note - if you have the money, swap in a MC or similar new/rebuilt transmission now and not have to do it later) I did this in fact with my 87 4Runner and it's still going strong. ($1500 4Runner for $600 with a dying trans - swapped and so on for $1100 and it's running great more than two years later.)
