It sounds like you're already narrowing down your options, but I wanted to share my setup as another low-cost alternative:
-Repurposed, low-end PC ($100 Dell off Craigslist for an i3-2120 machine with 500GB HDD and 4GB DDR3) (which is actually more power than I need)
-Rosewill 4U hot swappable 12-bay case ($150)
-Intel 1GbE Pro network card ($30) (better than motherboard mediatek chip)
-Currently using about 10 additional HDDs ranging from 3TB-5TB (for total available space of ~35TB) (prices vary)
-Windows Home Server 2011 ($40)
-StableBit Drivepool and Scanner combo ($35)
-Blu-ray/DVD drive ($60)
-MakeMKV ($50 for the full lifetime version)
Less than $500 total before hard drive costs. I have since upgraded to a Core i5 that I got for free that has AES-IN and some other neat features that I use to do some non-media related server stuff, but overall it's been a solid server. With the exception of a few bad 3TB Seagate HDDs, that is.
Using the above setup, I have backed up my entire Blu-ray and DVD collection (in addition to all my other files and media and Steam library) and can serve up any content to any PC or compatible device in the house (or outside the house using a VPN). Load XBMC/Kodi onto any PC or device, give it the path to the server, and it will automatically scrape media information upon startup. Click "play" to watch/listen. Easy. Likewise, any PC on the Windows HomeGroup can connect and play music, movies, pictures via any other software (VLC, Windows Media Player, etc.) you choose. Very flexible. This setup requires more setup for clients, but not much more.
The StableBit software keeps all my hard drives automatically load balanced, scans for bad sectors, scans SMART data, and automatically moves files off of problematic HDDs before they fail. You can choose to duplicate the entire array or select folders as many times as you want, depending upon how much space you have available. All my movies are duplicated once and all other files are duplicated twice or three times. Then I've also got a subscription to Carbonite for offsite backup. Unlike RAID setups, I can add or remove HDDs and they appear as normal HDDs in other computers and can be easily added or removed from the StableBit pool without issue. It's great software.