Learning Fretless Bass

How hard is it to learn to play fretless bass if you’re already an experienced bassist? Like 20+ years experience and I still like playing along with songs in my free time, so practice discipline isn’t really a problem for me. I also have a good ear, definitely have relative pitch. Having never tried it would I be better off picking up a cheaper bass to learn on, or just buy a good one (800-$1200 range)to start with?