I'm sorry but a 400w PSU isn't going to be good enough for a R9 280 that the OP said that he has already.
I think your build is a bit lopsided:
* 16 GB;'s isn't needed in this price range.
* The Corsair MX100 is overpriced for what you get. The BX100 is about the same performance and is about $30-40 cheaper. The Samsung 850 EVO that hovers around $100 is a better buy than the MX100, IMHO.
* The Corsair 200R is a great case, but at $65 is too much. It is usually around $45-50 (which, IMHO, is the right price for the case). I used a different option to keep the price within budget.
* Obviously you should have at least a quality 500-550w PSU for the R9 280, so there is a bit of wiggle room left over for any additional upgrades later.
Obviously there are many different ways to make a computer build within a budget and I'm not always 100% correct, so all of my suggestions are my opinions. I'm here to help, whenever possible
Here is what your build would look like with my suggestions: