There isnt really much you can really get with 200 bucks on its own. I know you cant really merge your gift but i would recommend spending your aunt's money on the Mobo for about $100. this only works if you get the remaining cash to keep. If so i would spend the remaining $300 on an i5 as they are a little over $200. This is all I can think of that seems like the best choice.
https://pcpartpicker.com/product/6kRFf7/gigabyte-ga-z270-hd3p-atx-lga1151-motherboard-ga-z270-hd3p
I would recommend this mobo which is about $130. this would theoretically leave you with $270 usd to spend. An intel i5 7600k will cost you $240 usd on newegg leaving you with a theoretical amount of $30.The slight price premium will allow for overclocking allowing for more performance and potential future proofing. Unfortunately you forgot to include a cooler but assuming you were using a horseshit imcompatible intel stock cooler i can recommend you a hyper 212 plus or evo which vary from $25 to $30. Best of luck and i hope it works out for you