If you want to publish said comic, you can't pay your team with "fun"
sometimes working in a big project with friends can be fun, but, if you expect serious commitment, you can't expect hobbyists to commit so much time and resources on your project.
Crediting people working for you is just a basic common decency thing and doesn't count as payment either, neither is the vague promise of "exposure".
When i recluit an artist we reach an agreement and i pay them for their services.....if one dude like me can save some cash to hire one artist, a group like yours should be able to afford to pay artists for their effort....