perform ajax query on a custom table or external data source

I have a very large table that currently exists in an external database (but on the same server) that serves as a lookup table for automotive products. I know the ajax implementation might be easier if I created a custom post type, but there are 92,000 records as it is. I don’t want unnecesarily burden the wp database. I’m currently just using cookies to maintain the values of each select box and the page reloads each time a field is selected, which is, of course, a bit annoying.