I need a seamless repeat pattern created from a drawing

I would like to make pj pants for my children and theirs friends. I have a drawing of a little red wagon that I would like turned into a seamless repeat pattern design. Ideally, I would like it created in Adobe Illustrator.
I was told this is an easy job for someone with experience but since I have no experience myself I'm a little unsure how to price it. Please let me know if you believe it is unfair.
Thank you!