I'm making a ULF pinhole camera, but running into the issue of f/stops in the triple digits. The other issue is that I definitely do not have the money for LF film, much less ULF film. Therefore, I'm using B/W print paper, which as I understand has and effective ISO of 3 to 12, depending on who you talk to.

I'm wondering if there's anyway to get that sensitivity higher. I don't care how grainy/contrasty it gets, I'd just like to push the iso to at least 25. Maybe using really high concentration developer? Are there brands/types of paper that are particularly sensitive?

Any information is appreciated. Worse comes to worst, I just have to deal with sunny day exposures ranging in the minutes, or softer pictures.