Super simple to get this one solo or with a friend. If you don't want to read the essay below here is a video
Load up the tutorial world, save exit and reload on easy. Then head to the South West corner of the map. Enter the building next to the pirate ship and get the Bow from the room with all the chests in it on the second floor. Grab a Bed from one of the other rooms while you're there. Then head back down to the pirate ship and grab a stack of Arrows from one of the cannons.
Head North from the ship and you should find a Desert Village. Put a bed down in one of the houses and set your spawn here (just incase you die trapping the skeleton). After this take apart one of the Sandstone houses and head to the flat desert section just west of the village. Make a tunnel that has a 1x2 block passage (so you can run through it).
Wait for night then punch a Skeleton and get him to follow you into the tunnel. Trap him inside and force him into a small section. Stand on top of the Block the Skeleton is trapped under and look at your map. Take note of the X axis number and walk 50 blocks in any direction (best do a couple extra just incase).
At this point SAVE YOUR GAME
. Turn around and take aim above the trap in order to hit the Skeleton from the distance. 3 hits laster and you should have one dead Skellyboo and a lovely 30G. If not reload and take a few sets back and try again.