Find a decent used PC that will accept either a 750ti/950, or preferably a decent used PC that has a PSU that has external PCI E power connector capability, and get a 1060 or something along that lines. $500 is possible, I find decent PCs here in Canada in the used sections for 250 CDN all the time, so factor in a reasonably new and powerful GPU like a 1060, and 500 USD is in sight for sure.