The GPU market right now is pretty crazy. Last gen are ending production, and the next gen are almost impossible to get ahold of. That being said, you should probably wait to get a new GPU if your old one is still working properly for you at the moment. As for that budget, there are not many options. More budget cards may be released soon, but the cheapest new GPU for the next generation is currently $400 US, though cheaper ones may be revealed later. If you really need one now, the GTX 1660 Super or GTX 1660ti would be the best fit, but you might be lucky enough to find a RTX 2060 for that price. I still recommend waiting for some time.