You have two options:
1) Enter these players as BandHelper users, and assign them only to the gigs they're a part of. They will only get emails for those gigs. They can use BandHelper with this approach, and you will need an account large enough to add all of them (but you can deactivate them if they're not playing for a while).
2) Don't enter those players as users, and track their pay as expenses in the Finance module. You can set up a Personnel category to track that, or set up a separate category for each player.
I use a mixture of both: option 1 for people who aren't full-time members but do join us regularly, and option 2 for people who only join us once or twice a year.