If it's a work machine I recommend buying a base Mac mini, then adding an ssd as a second drive and maxing the ram yourself. You will get a screaming fast machine for anything that isn't too graphics intensive like hardcore gaming. And it will probably cost you about the same or less as building your own hackintosh.
For me, it's just about updates and iMessage. I use iMessage a lot, and their security means it doesn't work on a hackintosh. Next are the updates. The issue here, is that graphics doesn't work, or the machine doesn't boot, etc. All fixable, but often you have to debug it once or twice.
Problem I had with the Mac Mini was I bought mine as the basic model, and its so slow to use, the hackintosh is better. However, nothing works as well as my MacBook for actual work.
Right now, personally, I'm waiting for the 5k iMac and when it can be used as an external monitor. I upgrade my computer every couple years, but my old Apple Cinema Display is 7 years old now, so I really need an iMac to be usable as a 2nd display. Hopefully september will bring that update.
I've moved most gaming to consoles, just not super interested in PC gaming and the iMac can still do most of it.
If Apple bring out a Mac Pro though with a gaming performance GPU I might consider that too, but thats never going to happen any time soon, lol.
Also finally I love the glassy reflective screens. Just so used to them these days and using anything but is just odd to me.
The only off-the-shelf PC I've seen used recently is a Gigabyte Brix (Gigabyte does make motherboards too but this is a complete computer).
Dell, etc. use their own BIOSes and while they may be compatible with hackintoshing, not many people are putting much effort into making them compatible. You may not be able to turn off certain instructions from the BIOS that cause crashes.
Avoid AMD processors and AMD/ATI graphics chipsets; not as much effort has been put into making them compatible.
One other detail- your legal OS X still has licensing terms that basically say if the box you install it on doesn't have an Apple on it, you're violating them.
Get an Nvidia Card (Any current model will work) if you want to avoid installation issues and get the best performance (Nvidia have native drivers for OS X) and make sure to enable TRIM on SSD's.
You might find these links useful in finding a compatible pc if you don't want to do diy:
http://wiki.osx86project.org/wiki/index.php/HCL_10.10.3/Port...
http://wiki.osx86project.org/wiki/index.php/HCL_10.10.3/Desk...
If I were you, I'd really go with DIY, fewer problems and you will gain experience.
johng linked to tonymacx86 which is a useful resource, although I don't really like MultiBeast since it's not actually the All-In-One solution it's supposed to be.
insanelymac.com is also quite useful :)
If you're looking to do development for Apple products though you're probably better off just buying a Mac.
As far as buying, the retailers will skimp on areas that are negligible or ignored by the consumer, e.g. motherboard, RAM, PSU. This makes it difficult to work with compatibility & OSX from a straight buy perspective versus choosing each optimized part in a custom build.
As a warning, you might run into issues with seamless integration that is normally experienced with Apple products via MBP/iPhone/iPad. The 'ecosystem' doesn't like Hackintosh :D
Seconding Korni22 and insanelymac forums.
It probably depends on your requirements. YMMV
If you're going through this to save a few hundreds, get a mba refurbished.