Not sure about the monthly-bill thing. It'd have to be content that I'd want to search multiple times a week, and I don't think there's any like that.
Maybe a better pricing model would be a set number of searches? $5 for 100 searches or something like that? That might align better with the costs, too.
The crawler is, arguably, the hardest part. We have open source search engines out there, like searx[1], but most of them are search aggregators, and depend on Google, Bing, and a few other established search engines.