I wouldn't put a new engine into a car with that many miles on it, unless I could do it for $2K or less. Today's cars are complex vehicles and, even with a new engine, there are many other things that could go wrong and leave you stranded on the side of the road. Just my $.02
Actually, the plan is to replace the 4Runner (wifey's vehicle) with a newer minivan
A bit of minivan advice, if you want it. My wife and I were looking at slightly used minivans this past June. We had a 1998 Plymouth Voyager that had served us well for 120,000 miles, but it was on its last leg and needed to be replaced. It also was a bare-bones minivan; smallest engine available, no power locks, windows or anything. We wanted something with more creature comforts.
We shopped around and test drove 2-3 year old minivans from Ford, Chrysler, GM, and Honda.
In the end we bought a
new Kia Sedona. It has power locks, windows, DVD player, seats that fold flat into the floor, heated windshield, cruise control, etc. Not fully loaded, but all of the popular features. 10 year / 100,000 mile warranty, 250 hp 3.8L V6 (quite a potent engine), all for $22,500 out the door. That's what the similarly-equipped
used minivans from the other manufacturers were going for.
Six months into ownership and 5,500 miles on the clock and we have zero complaints. There's nothing inferior about this minivan. I recommend you consider one when the time comes.