How much space does a DLC take on average?

Apologies if this has been answered before but I have an Arcade that I bought a few months ago and I think it's time to get a hard drive so I can download some DLCs. Fallout 3's Broken Steel is mainly what I am interested in right now but I might download a couple more DLCs for other games in the future. However, I'm kind of strapped for cash at the moment and seeing how I can get a 20GB hard drive for less than $30 on eBay, I was wondering whether that's good enough for what I want to use it for. With that said, I would appreciate it if someone can let me know much space a typical DLC takes up so that I have some idea of how much content I can fit on a 20GB drive. Many thanks in advance.

There really isn't an 'average' DLC size, it just depends on the game. For Broken Steel, I think it was around 650MB. For a 20GB HDD, I guess it just comes down on how much DLC you'll be downloading, since I have the same size, and have just about 8GB left after Fallout 3, Oblivion, Army of Two, both Gears, Fable II, Halo, and Mass Effect DLC.

That sounds pretty good. You have a decent amount of stuff with plenty of space left over. I think 20GB will be enough for my needs at the moment. Thanks for your help!