Ok, so Bit Fenix Prodigy = ~$90 = $760 remaining budget.
1) Do you have any components (ie optical drive or hdd) that could potentially be recycled to this build?
2) Where do you live? Near a Microcenter?
3) I would also suggest getting a quad-core CPU. i3 is fine for now, but probably not for long. i5-4430 for $190.
4) For an mITX rig, you need to play close attention to your specific needs. Keep in mind that mATX allows a few expansion slots besides the GPU, mITX...not so much...unless you've got an open mini card slot. Therefore, I'd recommend one of these boards
since they include WiFi. The biggest difference is that the AsRock mobo has an additional unpopulated mini card slot around back. Whether or not you need that is your decision. Most popular use for that slot would be an mSATA SSD, but you have room in the Prodigy for a 2.5" SSD anyway. Let's call that $145 for the budget until further notice.
5) RAM: One 8GB stick for $60.
That thing is 1600 CAS8 @ 1.35V and low profile to clear any future heatsinks. Having 1 stick now will still give you the ability to double up down the road without having to toss this purchase out the window.
6) 23" IPS monitor for $150.
Has good reviews, low price, better color than TN. I have this 5ms IPS monitor
and have never noticed any motion blur / ghosting
7) 430W modular PSU.
IIRC, newegg often has these on sale for $30. 430W will get you to a 7950 / GTX670 GPU
for future upgrades. Modular is nice for mATX / mITX builds.
8 ) AMD 7790 for $125.
Good power-efficient card, quiet cooler, good price.
9) 1TB hdd for $70
Save up for an SSD in the future, they're worth it. Then you can use this hdd as data storage.
System total including case, but without keyboard/OS = $870. You can get this lower by watching for sales.
I'm not going to make keyboard recs. I use a cheapo, others will probably try to sell you on mechanical ones. Optical drive....I don't use one. If you seriously consider it and think you need one, add $20 to my total above. Also you said nothing about an OS/Windows license. Does that need to be factored into the total?
Main: i5-3570K, ASRock Z77 Pro4-M, Asus GTX660 TOP, 120 GB Vertex 3 Max IOPS, 2 TB Samsung EcoGreen F4, 8GB 1600MHz G.Skill @1.25V, Silverstone PS07B
HTPC: A8-5600K, MSI FM2-A75IA-E53, 4TB Samsung SSHD, 8GB 1866MHz G.Skill, Hand-Built Wood Case