Hey, car stereo gurus

I’m looking for a suggestion for a 4" front door speaker that’s about $50 or less a pair. I know that’s not really much, but I’m refusing to get too snobby about this.
Also, I have a question about installing new speakers. My factory ones are mounted on bolts in a triangle, and all the aftermarket ones I see use four rectangular-oriented bolts. Is this fixable?

I replaced my factory front door speakers with equal diameter Pyle speakers-drilled new pilot 1/8" holes into the sheet metal and screwed them in place.