You should get your bike tires sipped too. :-)

 

They usually charge more for (re-)siping used tires since there is more chance of having grit and pebbles lodged in the tread. This can dull the cutters on the siping machine and that adds to the time needed to do each tire. Of course on an un-siped mud tire, that is sort of a non-issue. I still like to do my own, costs nothing, takes less time than taking the tires to a shop to have done and I can do it exactly how I want.