Building a custom search engine that can search 1000 websites at once

Question

I want to I build a custome search engine that has hundreds of websites. The problem with google's programmable search engine is that it becomes less accurate after 20 sites ""If your custom search engine includes more than 20 sites, the results may differ from the results of a 'site:' search on Google.com and your search engine may sometimes display fewer results." https://support.google.com/programmable-search/answer/70392?hl=en

Is there a tool that would allow me to search within 1000 site at once without affecting quality? If no, who can I find to build it? I prefer a one time payment (or pay per search request) than a monthly payment for the search engine (unless it's like 10$ per month or sth) . I'm not a tekkie btw.

I asked relevant experts, tried out different tools. nothing solved the problem up till now.