ooh goody finally a topic I'm an expert in..
for $2000 you can get massive amounts of storage.
I personally think it is wasteful to use an entire computer just as a fileserver. There is not much resource usage on one, as you are pretty much limited by the drives. I have a combined system using software raid. Currently there are 12 Sata drives in it, and one ide 2.5" laptop system drive. Total storage ~5.5TB
Also with the newest 2.6.24 kernel that will be out in the next month, sata port multipliers will be supported by default. Buy two sata sil3132 pci-e 2 channel sata 2 cards and you have 20 drive software raid (i'm already doing it but it takes a custome compiled kernel)
The sweet spot right now is the 750GB drives. For $143 a piece I bought some brand new western digital 750gb drives with 3 year warranty.
so cost breakdown of a kick arse file server or combo box
Case - Coolmaster Stacker - up to 20 drives in the front using 5in3 sata backplanes $90 @- http://www.directron.com/stct01ww1.html
5in3 sata backplanes - go for about $100 - here is a comprehensive listing http://wiki.lime-technology.com/wiki/index.php?title=SATA_Hard_Disk_Stackers
Power supply - something over 600 watts with active PFC to have high effiency. I'm using a 750 Toughpower
Mobo and cpu- amd or intel.. anything with low power usage and high reliability. Also the more pci and pci-e slots the better. Try getting one with built in firewire as well. I really like the intel E2180 chip as it uses very little power (12-18 watts in idle) it also overclocks to 3.5ghz easily on air if you need it to.
Ram - 2gb of cheap ram is fine. There is always a deal going on with HP ram for $7 per GB after rebate pc 800 chips
So pricelist so far
5x750gb drives in a software raid 5 - less than $750 also there are 4 internal ide spts in the included 4in3 in the stacker case, so you can buy a few more and include those in the raid5. If you use more than 5 disks in a raid5, I'd recommend having one set up as a hotbackup in case one fails.
stacker case $100
5in3 sata backplane - $100
power supply - $100
motherboard - we'll say $100
processor - again we'll say $100
ram - $20 after rebate
high quality power supply (do not skimp!) - $100
for 5 sata drives you can probably use on board without extra pci-e add on cards so free there
System drive - $50
total cost = less than $1420
As for a comparison of Samba vs NFS vs iSCSI
Samba transfer speeds over gigabit ethernet - Raid 0 - 7200 rpm sata 2 32MB cache drives - write - 85MB/s - read - 98MB/s - gigabit maximum is 125MB/s - I have dual bonded gigabit - adding a 2nd computer using the servers bonded ethernet - total write - 110 MB sustained writes, Reads- 138MB/s
iSCSI - write - 50MB/s with a much higher top processor/memory usage - Read - 70MB/S - iSCSI isn't a good standard. It's a resource hog - couldn't push it anyhigher using bonded gigabit
NFS - about the same as samba, but I get a lot of IObound errors when using it with myth. Gave up on nfs as samba is more universal.