The complexity of the case will depend on whether there are any issues that would raise concerns with immigration officials about the bona fides of your new marriage, and whether there are any issues in your past that could impact your admissibility as permanent resident.
Costs for representation vary. Call around, but focus on the firm's reputation rather than the cost.
If this is a good faith marriage and have sufficient supporting documents to prove it, you should be able to adjust your status.
This answer is of a general nature and should not be relied upon as final, nor is it intended as legal advice. Consult with a qualified attorney before making any legal decisions. Gen Kimura, (832) 247-6932.