I recommend to buy the parts your own and build it. Because 1) the asus PSU may or maybe not haswell compatible, if it does not you need go to the BIOS to change the setting then you can use it. More info
http://techreport.com/review/24897/the-big-haswell-psu-compatibility-list#antec and I add the link with similar price but with better GPU ( r9 270), more space for HDD, and better PSU ( antec Neo Eco 520C). For the OS, if you don't want to over that budget, then get the R7 260X that is cheper gtx750ti but has same performance.
r9 270/r726x/gtx750ti review
http://www.tomshardware.com/reviews/geforce-gtx-750-ti-review,3750.html
You can change the store/site to buy the components too, because I don't know which site is good for you.
PCPartPicker part list:
http://ca.pcpartpicker.com/p/3gQDS
Price breakdown by merchant: http://ca.pcpartpicker.com/p/3gQDS/by_merchant/
Benchmarks: http://ca.pcpartpicker.com/p/3gQDS/benchmarks/
CPU: Intel Core i7-4770 3.4GHz Quad-Core Processor ($328.75 @ Vuugo)
Motherboard: Asus H81M-A Micro ATX LGA1150 Motherboard ($65.99 @ Canada Computers)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1600 Memory ($82.90 @ DirectCanada)
Storage: Seagate SV35.5 1TB 3.5" 7200RPM Internal Hard Drive ($74.25 @ Vuugo)
Video Card: Club 3D Radeon R9 270 2GB Video Card ($199.99 @ NCIX)
Case: Zalman Z9 Plus ATX Mid Tower Case ($47.99 @ NCIX)
Power Supply: Antec Neo Eco 520W 80+ Certified ATX Power Supply ($59.98 @ Newegg Canada)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer ($16.79 @ DirectCanada)
Total: $876.64
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-03-26 14:28 EDT-0400)