We use a seagate blackarmour 440, 4 x 1tb drives running raid 5 so 2tb of usable space, theyre quite affordable now (under £250) if you look on ebay and amazon etc, only issue is disk read speeds (we use it as a media server) and if more than 2 people are streaming HD movies at once is does struggle as the standard firmware only allows for read/write speeds of 10MB/s. Some of the synology nas drives are bloody fantastic for the price, worth reading some reviews etc and find one that suits your needs as obviously some a great for storage and redundancy and others are better suited to being a mediaserver, alternatively build a low spec desktop with support for RAID 5 and say 8HDD's, you could combo up 8 x 1tb drives and get yourself 4tb of usable space with decent redundancy!