3" seems to be a sort of standard faucet spacing. You can find drip trays with pre-drilled backsplash at that spacing. I spaced mine at 3-1/2" on center which allows glasses to sit side by side under the faucets. You can find pictures in this post:
I bought a basic stainless drip tray, built a frame for it, and attached it with some strong magnets.
