Your're gonna need a higher budget than 100. I would of just completely built one yourself. There are many videos on the internet showing you how to build a PC. I suggest YouTube. The users LinusTechTips or either Jayz2Cent(or whatever it is).
I Suggest, if you're going to build a PC...
-Quad-Core Processor (or more cores)
-Four 2 Gig RAM Sticks(if you get the full size board with 4 DIMM Slots)
-A Dedicated Graphics Card
-600 Water Power Supply
It's much cheaper if you build it yourself, believe me.
And why exactly would he need four 2GB RAM sticks? No mainstream platform is quad channel and AFAIK there are no 2GB DDR4 sticks in the first place. Only X79 and X99 have quad channel memory controllers in the consumer market.
On all mainstream platforms excluding AM1, which is single channel, the memory controller is dual channel, meaning that if you use 2 or 4 RAM sticks, you can operate them in dual channel mode which increases memory bandwidth. There is ZERO benefit to going to 4 sticks from 2. The only situation where you would go to four RAM sticks would be, for example, if you already had a pair of 16GB modules and wanted to add a second pair of 16GB modules. Adding more sticks puts more stress on the memory controller and it's best to use the fewest sticks possible.
Buying 4 2GB sticks would put more stress on the IMC, it would also be foolish as you would be taking up all four slots with extremely low capacity sticks of memory.
Also why does he need a 600W power supply? You don't even know what the rest of his system is. What if he wants to go SLI/CFX in the future? wouldn't he need more than 600W? What if his system consists of a 60W CPU and a 150W GPU? Does he really need 600W?
The best build videos on youtube btw are by carey holzman. Check out his channel.
OP, check how much room you have in your case, and if it'll fit, pick up a GTX 1050. You shouldn't have to change power supplies for that card, and it is about 100 pounds.