Keep at it. You're at the lull point between common metals and more exotic goods that requires you to tangle with some bosses who are kind of poorly built (at least, that's what the Devs have been saying lately).
It gets better once you're over the initial hump of bosses. The dungeon is full of great loot and Hell is fairly interesting. There's also the underground jungle worth considering (and really, you could do that now and get some more loot).
All you need to do to spawn the Eater is smash some Shadow Orbs. If you've killed the Eye of Cthulu, you can get the Dryad to move in. She sells Purification Powder, which turns Ebonstone (the dark stone in the corruption) to normal stone. Alternatively, you can get a rotten chunk (common drop from devourers) and vile powder (made from Vile mushrooms) to make Worm Food.
To get the Nightmare Pickaxe, all you need are 6 scales. Each segment of his body can drop up to three and he's made up of quite a few segments. Once is all you'll ever need, honestly. Even if you don't defeat him, you'll probably still get enough scales from the fight that you won't need to. Unless something has changed, the Eater usually despawns if you take too long or die.
Once you've got the nightmare pickaxe, it's a quick jump to Obsidian (for an obsidian skull) and then you can move to Meteorites and Hellstone.
