Maybe if you provide more info, like how much capacity you need... I presume by "slow" you mean that it doesn't need a powerful CPU?
I just picked up a server from Techiemedia with 4 x 1TB hotswap drives. Most hosts should be able to give you a 4 drive chassis which means you could (currently) fit 8TB of raw storage into a single reasonable priced server. Then there's the cases with 20 bays, but they cost a bit more.
