Start up would be about $250 if you have to buy retail, but you can do much better buying used, maybe as low as $50 if your timing is right. The first thing you need is a reloading manual, I'm familiar with Speer and Lyman, others are probably equally good. This doesn't need to be the latest edition, but it needs to be followed religously. You'll want a good press that takes standard 7/8X14 thread size dies. Some older presses take smaller dies, avoid these like the plague. Mine's an RCBS, very common and reliable, but almost all popular brands are good. Figure about $50 bucks for a good used press. You'll want dies, and the proper shell holder to fit your press and caliber of shell. Most companies make very good dies, but make sure they're the 7/8X14 thread size. Figure ten to twenty bucks for good used dies in the popular calibers, way more or way less for the oddball ones, depending on how motivated the seller is. A powder scales is a must, and a good powder measure will be wanted very soon, but you can reload only using the scales, it's very slow to do it that way though. Figure about $20 bucks for a used scales, ditto for measures. You want a loading block to set the charged shells in before the bullet is seated, this can be store bought or easily improvised as a block of wood with holes drilled in it. You'll want a case lube pad to lube cases prior to resizing, they are cheap, but a stamp pad works too. Before too long you'll want a case trimmer to restore the case length, figure another twenty bucks. Shop at gunshops and gunshows, or you might get lucky and catch a guy selling his whole setup at a garage sale for a rediculusly low price. Usually with a half a can of powder, primers bullets, empty cases, etc. This is how you can get started for $50 bucks, but you may have to wait a long time. Ebay offers alot of this stuff that generally goes at the high end of used equipment prices, but it's easy to find that way. In fact, (warning! shameless plug comming) I have a powder measure and case trimmer on there now

If your talking shotgun reloading, all you really need is the press and a good reloading reference book, a powder scales it a good idea too, to verify powder weights.