The problem with search engines is that people think it's just tokenizing the search query and then doing an AND query for the words, but then the fun starts. First of all, there is specific search theory that one has to dive into and have the Knuth tomes nearby. Then, different languages, thesaurus, taxonomies, "did you mean". And we are not even at indexing speed, replication, performance, etc. There is absolutely no chance you would be able to create and maintain a reasonably good search engine part time.