in cabin air filter

My 2000 with 65k on it is at the dealer for service. They want to replace the "in cabin air filter" at a cost of $100. This seems pretty expensive. Will not replacing this filter harm the mechanical perfomance of the heating/cooling system? Or will it just cause me to breath some dirty air? Is this filter one that I could easily replace myself? Thanks

dealers usually charge too much for their parts. you can probably get the filter somewhere else and install it yourself...its not that difficult to install.