I would pay up to $120 per month for a search engine that had its own crawler, and was completely open source, as long as it worked with JS disabled.
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.
[1] https://github.com/asciimoo/searx