Price is alway an issue. You are using the space so you should invest in decent storage capacity. I personally spin about 15 SATA drives off of a single raid card.
I recomend the following:
Build a decent NAS head with the following recipe and share it out to all your other devices.
buy a 4U case with ~ 20 drive bays that link to a SATA bus ~$300 (http://www.newegg.com/Product/Product.aspx?Item=N82E16811219041)
-You may need to mod the case if the port multiplier is SAS instead if SATA
buy a high point RAID controller in the 2000 class or higher (http://www.newegg.com/Product/Product.aspx?Item=N82E16816115049) (32 drives max with 4 port port multipliers and mini sas - 4 sata cable)
Start with 4x 2TB drives (RAID 5, 3 + hot spare)
1 gigabit ethernet hub
then attach it to a cheap cpu with a good amount of ram and gigabit ethernet. Stick the storage kit in the garage and run cat 6. Put the hub in the house and wire it to any machine playing back HD video, for the rest I find you can get away with wireless G.
You are looking at about a 1K investment in kit for storage. For OS I'd use your favorite flavor of linux, gentoo for me but I recomend deb or ubuntu for other people, that supports lvm. This way you can add new drives and expand the storage dynamically. You can expand ext3 or ext4 easilly, you just can't shrink them. In my opinion there no need to go exotic with the FS.
Once you set up the storage share is both via nfs to anything playing high def content and samba for everyone else. Then sit back, relax and enjoy.