Cheapest Harddrive Solution that works?

gotta look up the specific model number and version number to know if a router is dd-wrt or otherwise 3rd party compatible. especially linksys. often the same model has 3 or more different versions with different chipsets. make sure you read the wiki for the 3rd party firmware good and you know exactly what you are buying. some routers may never run 3rd party firmware and some of them look identical to routers that are extrememly popular for 3rd party firmwares..

If you are after CHEAPEST, thumb-drive is the way to go. No moving parts comes as a bonus.

I run my MechMate off a 8GB thumb-drive for nearly 3 years, from Ubuntu 8.04/2.4.6 to 10.04/2.5.
Simple breakout board on parallel port, Intel 945 with Atom 230, 1GB RAM, 15" LCD, Keyboard+mouse.

Boot up slow & reading file slow; Apart from that, no issue, never had any crash or stability problems after everything were config proper.

But off late, a friend gave me a cheap 8GB SATA2 SSD SLC type, I'm in the process of refitting, will try it out when I figure out other bits which to upgrade/change.