I'm in the middle of swapping a 350 into my '98 TJ, so I can tell you what I've run into so far.
You'll need the engine, obviously. I'm rebuilding one from an '82 pickup that I got for $200. We've sunk about $1500 into it so far and will probably add another $500, but by the end we'll have a custom built Vortec monster. If the one you've found is running well you could put it straight in, or do a quick and dirty overhaul to make it run like new and squeeze a little extra torque out of it. If you don't have the time/ability to rebuild, you can get a decent new crate engine for anywhere from $1500 to $5000 depending on what you want and are willing to spend.
I'm swapping out the 2.5L 4 cylinder from my Jeep, so we'll be replacing the flimsy stock transmission with one capable of handling the power being added. Check www.novak-adapt.com
! They have a host of rebuilt transmissions for sale along with adapter plates to bolt any transmission to any engine and any Jeep transfer case. They also make engine mounts for putting a Chevy small block into a Jeep, so you'll need to get those and have them welded in.
Good luck with the swap!