Someone quoting $500 doesn't want the job. The most expensive tires you can buy in the size used for vans and van cutaways should be under $300 installed and you might find cheap tires close to half that.
In your area there are tens of thousands of vans and small commercial vehicles using the same tires, so there must be tire dealers that service them. This work is often done outside, places like Walmart, Sears etc often have a policy of not working on anything that can't be brought in and put on a lift. A Chevrolet or Ford TRUCK dealership will do the job, but maybe not at the lowest price.
I like to buy my tires through an alignment shop that does medium duty trucks, because an alignment check (but not realignment) and brake inspection in included with tire installation. I pay about 10% over Tire Rack wholesale, which is a bit under Tire Rack retail Internet prices, for the tires, mounting, balancing, and the inspection freebies.
No specific recommendations for San Jose, but I know what kind of place to look for, anywhere. It will usually be along the highway or near a truck route through town, or in a light industrial zone, not in strip mall or shopping center annex.
