I run a small search engine with its own crawlers and about a million listings. I really haven't done much with it for about 2 years, but it has gained in popularity to the point where I feel like I need to update the site to make it work better for the end user. I think its simple straight-forward design gives its users what they expect, and that keeps them coming back. I also sell premiere listings on the site and it is reasonably profitable.
I've been thinking that I need to connect with a major search engine to use their results as backfill, but after an hour or so looking over API's from the majors and their TOS's, I have not found anything that will work.
FYI: Google allows 1,000 queries to non-commercial sites, Yahoo doesn't allow me to place non-Yahoo listings with their listings, and MSN's program doesn't seem like it's mature enough to be stable. I've tried some of the PPC services as backfill, but their resultset is even more limited than mine.
Does anyone have any suggestions? I think it would stay under 10,000 queries a day for the foreseeable future.