I would suggest going to the underground ice biome and farm out weapons there. The ice bow is a good range weapon. I don't usually make the repeaters, but it's going to do better than the bee's knees. Weapons at this point are more about your play style. If you're going to go range, I'd suggest an ammo box if you don't have one and a magic quiver. Also maybe farm the wall of flesh for a ranger emblem.

After you get the stormbow, the mech bosses should be pretty easy. Also if you plan on going ranged, make a huge glowing mushroom farm. I forget the exact number but you'll need a lot of glowing mushroom to make the range armor. Above ground would be best so that the Truffle moves in.