Is there a way I can divorce my incarcerated spouse for free or low cost?

It should not be a major case unless it is contested, and therefore not terribly expensive. You, however, cannot expect an attorney to work for free, do you?

You might call Legal Aid and see if you qualify for their services.

You can always ask for a waiver of fees, but if you have a job, chances are you will have to pay the filing fee. File your complaint, get it served and see what happens. If your spouse doesn't answer, you can probably get a default judgment. That will be about the cheapest.