Your best option for a swap is going to be a 5.0 from a 96-01 Explorer. It will be a virtual bolt in swap with minimal wiring changes compared to anything else. Not saying its going to be easy, but probably the easiest. The best way would be to buy a wrecked Explorer with the whole drivetrain and have them sitting side by side so all the little parts are available.
I have a 2000 Explorer with a 5.0 already and I was going to do the swap, as well as swap my 4.0 back into the old Explorer so it could be sold, but had to abandon it as I just don't have the time right now. About the only thing I could think of I'd really have to pay for extra this way is to have my exhaust done, buy a driveshaft for the Explorer ($50 from the JY) and have the ST driveshaft modified to fit since it never came with this drivetrain combo.