I've found the best early(ish) way to make money is to farm the Eater of Worlds, he drops over 99 Demonite per encounter, which sells for rougly 8 gold a stack. If you use a Vilethorn he's extremely easy to kill repeatedly. The only part about this is getting enough vile powder to repeatedly summon him, but such powder can be bought from the dryad during a blood moon at the price of 1 silver per powder. IE: 30 silver per summon, with each summoning gaining you almost 8 gold. So it easily pays for itself if you drop 3-5 gold into vile powder. Between that and a mediocre Vile Mushroom farm you should be fine. The EoW drops enough rotten meat himself to supply that half of the crafting reqs for the Worm Food to summon him.