Bushpilot is right. There are two places that are "competitive" (not cheap) on the filters. Your only other choice is to go to the dealer--but it will cost you a lot more. I order mine in large quantities, as they ship for free on larger orders.
Beyond that, there is nothing "cheap" about owning a diesel--especially now that diesel fuel is more expensive than reqular gas. The value factor comes into play when you tow and cross 150,000 miles and you don't have to replace the truck.
In summary, I don't know of any vehicle is cheap to own anymore. Fully loaded a vehicle is going to cost you about 65 cents a mile for the first 100K miles (averaging 20,000 miles/year for five years). That's the reality--and the government allows reimbursement at 40.5 cents.