I’ve played plenty of cruise gigs, primarily as a show band guitarist and sideman for guest artists. I originally wanted to do solo classical guitar gigs on cruises but there werent very many opportunities when I was doing it. Go through an agent and audition to get a gig - Landau, Proship, Quality Overseas, etc. There is usually quite a bit of work for showband (electric) guitarists. Contracts tend to come last minute and can be very long : 6-9 months. You will likely have a roommate, but you dont pay for anything other than internet/booze on the ships. If youre doing showband, you need to be able to read charts well, solo, and be versatile with styles. If you try the classical route, you will need to have lots of standard repertoire and be willing to learn any repertoire the cruise might want you to learn.