I started with $1,500 (for my first site, not this one. This one I invested a LOT in early on - not all of it prudently!) so you don't need a ton to begin, especially if you're willing to invest a lot of sweat equity.

But you do need a little bit to fuel the fire.

I think bare minimum you need to register a company which costs $10 or so, dropshippers you want to do business with expect you to have that paperwork. That's enough to get you started dropshipping on eBay or something similar. You'd definitely be smart to spend a little more setting up a site with a logo, but it's not hard to get Opencart running and you could create a simple logo with open source editing software.

If you really did a lot of the work yourself I'd say you could get an eCommerce site up an running for $20-30 depending on the domain name and hosting options (many of the lower cost hosts expect you to pay a year subscription up front for the lower cost hosting options, so it would make more sense to pay more in the beginning to get the lower rate).