Going rate for filters at the dealers near me (Chicago suburbs) is between $5 and $7.
Another good online source is
http://www.irontoad.com, but they've changed their web site recently. It's heavy on accessories, and a lot of the filters and maintenance items have disappeared. They can provide filters and things at good prices - $4.42 for a filter - but you have to "get a quote".
For a filter or two, it would be really hard to justify the shipping cost. For more expensive parts, the savings will probably make the shipping worthwhile.