Can I get a divorce for free if husband is incarcerated?

There aren't special free benefits just because someone is in jail. Pay the fees if you want divorced... everyone else has to.

If its uncontested it won't be as expensive.

No, if he will not contest it, you can file the paperwork yourself and just pay court fees,
Or hire paralegal to do the paper work.

If he contests and/or if there is issues to fight over, it will be a regular divorce