Which mail forwarder in South Dakota should I choose?

I am thinking of switching my driver's license to South Dakota. What is the least expensive mail forwarder? Or which do I use? There are many to choose from. I only plan to have three or four pieces of mail per year forwarded, so I am low volume (Motor Vehicle stuff and insurance only); the rest of my mail goes to relatives or my preferred private mail box pout of state. (When I contacted SD MV, they said you have to have a mail forwarder *in* SD to get a DL there, not a mail forwarder or relative out of state.)

Thanks!