CrossFire (Multiple AMD GPU) doesn't always scale very well and isn't supported in many games so i would recommend upgrading the CPU to an i5 7600K (Update your BIOS first so it can use the newer generation CPU). Additionally, i would recommend getting 16GB RAM if you don't already have that much or more for gaming. The i5 should go well with the RX 480 and will fit into your budget well. Hope this helps
*Edit* It's $325 at PCCG and i would use the remaining to grab a nice CPU cooler if you are using the stock Intel one as the K series can get quite warm and it will allow you to overclock for more performance in the future if you need.
Link >
https://www.pccasegear.com/products/37425/intel-core-i5-7600k