There really isn't anything better for that cheap. Most upgrade options would require a new motherboard and new RAM, significantly increasing the cost and ensuring that it will go above the $200 mark. Other than scouring eBay for a used Haswell i7s eg. 4770, 4790, or their K variants, or looking for used Xeon E3 1230 or 1231 v3s there aren't any other options.