Speaking as a freelance artist,
It's best to pay the artist something. In fact, it's the right thing to do. Comic art is a lot of work and the artist puts a lot of time into making it look good. Art is an investment and if the project is important to you, you should be willing to invest some $$$. It's about making your vision a reality so you can impact others.
If you are presenting to a ministry, save up, get a good artist then pitch it for publication. Then you can make good on your promise for increased profits should the project take off. Investment is a risk like that.
BUUUUUUT, if an artist wants to volunteer for your offer, far be if from me to hinder them :-)
All the best!