First off to build a 250 fps computer is a waste of time and money. It's like buying 4 gallons of beer when all you have is a 1 gallon bucket to take it home in...
I assume your monitor runs at 60 fps, with that in mind a single GPU will be fine (running everything on Ultra and maintaining 75 fps). Your screen size will also effect your fps...keep that in mind.
The best way is to get a "Barebones" kit, here is a good example of one for 550 dollars....
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=9584391&CatId=31
INTEL 4690K/MSI Z97/8GB/120GB/500W/CS
This Bundle Includes:
Intel Core i5-4690K Processor - Quad Core, 3.5GHz (6MB Cache, up to 3.90 GHz), 2 Memory Channels, 16 Max PCI Express Lanes - BX80646I54690K
MSI Z97 GAMING 3 ATX MOBO - LGA 1150 socket, Intel Z97 Express Chipset, 2x PCIe x16, USB 3.0, VGA, HDMI, DVI, DirectX, Crossfire Ready
Kingston HyperX Fury Red 8GB Desktop Memory Module Kit - 1866MHz DDR3, CL10, DIMM - HX318C10FR/8
OCZ ARC 100 SERIES - 120GB, 2.5", SATA III, Solid State Drive - ARC100-25SAT3-120G
Thermaltake VM30001W2Z V4 Black Edition Mid Tower Gaming Case - ATX/MicroATX, USB, Audio, Blue LED fan
Ultra LSP Series V2 650-Watt Power Supply - ATX, 6x SATA, 2x PCI-E, 20/24-PIN, Thermal Controlled,135mm Fan, Single +12V Rail, Short Circuit, Over-Voltage and Thermal Protection, 3-Year Warranty
Now all you need is to transfer your old hard drive to this computer, install your games on the SSD and a decent GPU like...
MSI GeForce GTX 960 Gaming 2G OC Video Graphics Card
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=9596384&Sku=RSC-102842348
This one will cost you 230 dollars
Enjoy and post up any questions,
jn