Something like the 6600 or 6600xt(or 6650xt) could be the cheap alternative you are looking for as they cost around 200 dollars and give a decent performance bump for you.
A used 5600xt would be a much cheaper but somewhat sideways upgrade as it sells for around 100 dollars(according to Hardware Unboxed’s last gpu pricing video) and offers a small performance improvement of 5-10%.
Side note - in my view, the sideways upgrade to AMD from nvidia may not be the smartest use of money. AMD’s advantages over nvidia are real but unless you really do need a new GPU(because you are using the 1660 super for another rig or giving it to someone), the advantages are nowhere near large enough to justify buying a new GPU of around the same performance level. Of course this is just my viewpoint and you might see things differently