Equipment? You can be reloading for not much more than $100. From there, it depends entirely on how many body parts you want to sell.
With a Lee Loader and a hammer, you can turn out perfectly good ammo. In return for much lower cost, you invest a bit more time and elbow grease.
A starter kit from one of the major manufacturers will have a single press, scales, lube equipment and so forth. That's sort of entry level above Lee Loaders (you cannot upgrade from Lee Loader to this, BTW).
Then you can add other stuff such as an automatic primer feed, case trimmers, etc. You won't need those initially, but will soon realize their benefit.
Top-end is a 'progressive' setup, in which you are kindasorta into factory production. Every time you pull the handle, a complete round drops out. Very cool, very efficient, very expensive.