Might buy a 1995 Jeep Cherokee Sport.
Seller says it runs perfectly. It’s just that if theres more than a half tank of gas it has a slow drip. It is automatic.
Can this be cheaply patched? If not, ballpark cost to repair?
New aftermarket fuel tanks are available.
I have been successful with an epoxy gas tank repair solution available from most auto parts stores.
How many hours of labor will a mechanic bill if I don’t DIY ?
On some AWD cars you have to remove the rear differential but I don’t think that’s necessary on a Jeep.
It just involves removing some bolts, disconnecting some hoses, removing straps, j-bolts and lowering the tank. It isn’t particularly difficult.
The labor guide shows 1.1 hours plus time to drain the tank if necessary. A fair labor quote would be 1.5 to 2.0 hours.
Be aware that if a shop won’t use your part an OEM tank is more than $500.
I would also figure in a new fuel pump and filter. It would be foolish to install a new tank on an aged vehicle and not take care of the pump while the tank is out.
Ignore the pump and said pump will fail in the middle of nowhere 2 weeks after installing the new tank. Mr. Murphy says so… 
Nevada, is that labor guide online somewhere?
ok4450, good idea about fuel pump, filter, and exposed fuel lines.
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It depends much on the local cost of labor. Years ago I had the gas tank replaced on my 1984 Impala. The labor of fixing it properly (similar leak as OP) was more than just getting a new one. It set me back $365 at that time.
The $500 sugested is about right. If an easy fix is possible, by all means do it.