My needs are a bit unique. We have around 500,000 products in our database. Each night we update product information in a batch like process. I have tried all of the major search plugins, but none of them work the way I need them to work.
So I wrote my own solution. I have written other plugins, but could not figure out how to implement a search plugin - so I changed the base code all over the place creating an upgrade/ maintenance problem for myself.

I don't have any interest in competing against the already viable search plugins, besides my solution relies on a 3rd party (paid) search engine making it not very appealing from a cost stand point.

I would appreciate any comments on how to create a search plugin.

Thank you!