Probably the most lucrative gigs for a purely instrumental band are Dance Band ones. This does mean having a suitable repertoire, having a caller (or knowing a few) and being willing to play at a suitable speed for dancers. There's plenty of bookings around for a capable band and caller, but it can be quite hard work.

Most folk clubs don't really want to book a non-singing band for a whole evening, but some pubs might be willing - the money isn't likely to be anywhere near what you'd get for the average Barn Dance though.