You could even run a single instance of Everquest on pretty much any regular CPU from last 10 years with 2GB or RAM + plus some sort of GPU from last 8 years.
That said I would recommend getting at least a 2nd gen i3 preferably 3rd or 4th gen.
If you want to single box on Phinny for $100 then something like this with Ivy Bridge i3 would be perfect:
http://www.ebay.com/itm/HP-Elite-83...GHz-4GB-500GB-HP-Warranty-12-16-/152129468498
Small, plenty of CPU power, doesn't eat much electricity, plus Ivy Bridge integrated graphics are good enough for Phinny.
Because it is a dual core, 4 thread setup, this would not be good for more than 8 boxing on a regular server with say 8GB of RAM.
If you plan on adding a GPU then look into medium sized SFF boxes from HP, Lenovo and Dell, again anything from 2nd gen Sandy Bridge i3 and up should be plenty of power.
This same seller has Sandy Bridge i3 for $80:
http://www.ebay.com/itm/HP-Elite-82...tel-i3-3-1GHz-4GB-RAM-500GB-HDD-/162097557020
Only problem is that you can't add a graphics card to these USDT cases so I'd prefer the Ivy Bridge integrated graphics for $20 more.
I am slowly moving away from my i5 setups to i7 setups because multi-threading does help when you are running 16 instances in a single box.
I run 16 instances on Ivy Bridge i5 with integrated graphics but there are glitches sometimes. Haswell i5 has about 2x better GPU integrated.
Again, I pay 20 cents per kWH so to me the electricity costs are important.
If you live where electricity is cheap then by all means buy the first gen i7s + GPUs like Razkle does. Those are generally $50-100 cheaper than 2nd gen.