How hard it is going to be is subjective, depends on how good you are with a wrench. It will be harder if your not the one who took it apart, you might want to try and find someone you know who has a Explorer of about the same year to make sure everything gets put back where it belongs. I would myself buy this truck, if I could get it cheap enough. With no heads if it's 2wd I myself would pay maybe $200ish, with 4x4 $300-450ish (just because 4x4 is worth so much more then other places in the country here in the midwest). Not a penny more, and probably a whole lot less. That would depend on what shape the rest of the truck was in. 118k isn't bad at all for these trucks. Course take into account if you do put it back together that head, intake, and valve cover gaskets are not exactly cheap. And heads are not your garden varity shade tree fair, really it comes down to how much you know about cars yourself.
If you can't do it, and have to take it somewhere, expect a bill in the range of $600-1500 to put it all back together. Also if you can't get it you maybe able to sell it, but if you junk it you will maybe get $200, (you could part it out for more and make quite a bit) here in the midwest. So if you can do the work yourself it's maybe a good deal, if not, look for a running one you can buy. The only other consideration might be if you buy it cheap, you can put a little money in it at a time and not have to drop the whole wad at once, that's one plus.
