Try some high-speed steel burs. They typically are cut to lower standards of quality; the diameters can vary a bit and their angles and height of the cutting portion can vary, but the flutes are deeper and more coarse, so they don’t tend to clog as much as higher priced burs do in softer metals. They also tend to be cheaper than their high-quality equivalents
Use a light touch and use plenty of bur lube. Don’t let them get hot and they can last a surprisingly long time.