PSU wise, I will leave that one up to you, but head my warning!! Do not skimp on the PSU, you will get what you pay for, I suggest sticking to the favored brands (and personally recommend corsair, I have had several and not one has ever died on me)
Personally I would save up and build a nice rig why pay a little, when you can have more fun and pay alot
If you want to spend a little more, but still within budget I run x2 of these (Although one would do) and they are not bad, although I am in the middle of upgrading my rig and these will be going, mainly because they are heavy and actually bend my pci slot (But not so much that they will break), but great value for money and veeeery quite. But this will get you full everything, as long as your CPU can keep up, your are on the limits with your current one.....I dont think your CPU will handle 60fps on ultra @ 1080p when all hell breaks loose in game.
No matter how much you spend you're not going to "play the game at 1080p at ultra with 60fps", your CPU is simply too weak, even high end CPU's can't get 60FPS in many situations (LFR, places with lots of people etc.)
As myself and Notarget have mentioned, your CPU is a little on the weak side. I have my I5 @ 4.47 ghz with x2 GPU (although starting to think its a curse) and I still get the odd stutter when things go a bit....graphical, things like Sha still make my fps drop (Although not 100% sure that's a hardware problem)
If you do go forward and buy upgrades, go with Notarget, but I disagree with the ENERMAX NAXN 450W, dont get anything that isn't 80+