Hi Steve,
I figured I'd chime in since I've done this job on an older (ZJ chassis) Grand Cherokee, and I've got this newfangled account here... Might as well use it.
A couple points... If you can find a reputable shop that will do it in 7 hours (and will guarantee you'll only be billed for 7 hours work), take them up on the offer! Replacing the evaporator (or heater core) is a very intensive job!
The evaporator is inside an airbox that is bolted to the firewall of the vehicle (the big piece of metal separating the cabin from the engine compartment). Access to it requires the majority of the dashboard and dash components to be removed from the vehicle, an A/C refrigerant evacuation and refill, and even the coolant system will have to be partially drained, refilled, and purged of air. In addition, there are several servos, cables and doors that are associated with the automatic climate control system that all have to be removed and reinstalled... Correctly.
In short, it's one of the biggest PITA automotive repair jobs one can untertake. Lots of disassembly, lots of bleeding knuckles, and lots of potential for things not going back together right (leading to dash rattles, HVAC control issues, etc.), requiring another tear-apart to satisfy the customer.
Many shops simply refuse to do evaporator/heater core replacements!
There is one potential "quick fix"... If the evaporator only has a pinhole leak, and a competent tech is able to finagle access to it while installed in the vehicle, a dab of JB Weld will seal the hole. That said, if you have a leak one place, another is bound to crop up elsewhere soon, and make your band-aid repair useless.
I'd expect to spend somewhere between $700-1000 in parts/labor by the time you're said and done... And expect a few newfound dash rattles, as the whole shebang
never goes back together perfectly.