I will assume you have a PSU and case because you haven't listed them here so, this is what I recommend:
AMD Ryzen 3 2200G -
https://www.amazon.com/AMD-Ryzen-Processor-Radeon-Graphics/dp/B079D3DBNM/ref=as_li_ss_tl?ie=UTF8&qid=1546001647&sr=8-1&keywords=2200g&linkCode=ll1&tag=xm3a06-20&linkId=38b1a417d2212833f45d9742a921eb7d
ASRock B450M - https://www.newegg.com/Product/Product.aspx?Item=N82E16813157842&ignorebbr=1&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-PCPartPicker,%20LLC-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
G.SKILL Aegis 8GB 2666MHz - https://www.newegg.com/Product/Product.aspx?Item=N82E16820232722&ignorebbr=1&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-PCPartPicker,%20LLC-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
Crucial MX500 500GB -
https://www.amazon.com/Crucial-MX500-NAND-SATA-Internal/dp/B0784SLQM6/ref=as_li_ss_tl?ie=UTF8&qid=1546001686&sr=8-1&keywords=mx500&th=1&linkCode=ll1&tag=xm3a06-20&linkId=56d784b32415ddd48177596b862dd5fc
PowerColor RED DRAGON Radeon RX 570 - https://www.newegg.com/Product/Product.aspx?Item=N82E16814131717&ignorebbr=1&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-PCPartPicker,%20LLC-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
So... the same CPU, better motherboard, better SSD, better RAM, better GPU, and no HDD, I decided to remove the HDD because I peaked you a 500GB SSD for a good price if you want to buy the HDD then you can of course but it will be above the budget you have.
Total costs: 427$
Total costs with HDD: 472$