check tucker tire. they have sold me the least expensive tires, with tubes, on rims, shipped to my door that I could find new. in fact.. they beat the price my local farm tire store offered for tires alone!!.. no tubes or rims!!!
past that if you need used.. check ebay and craigslist. i scored a set of 11.2-28 tires on rims with centers plus 6-16 tires on rims ( 8n running gear ).. on craigslist for 250$ the other day. grabbed them as spares...
soundguy