I haven't used them yet, but the University of Louisville's Micro/Nano Technology Center has competitive pricing. They guarantee down to 6um and depending on the design can hit 4um. It's $375 for a 6x6 and $225 for 4x4. 1um is billed at $100/HR and was told that a 4in plate would take several days.

https://louisville.edu/micronano

After the next prototype run, I'll probably use them or MIT's Nano Fab lab.

Thanks, do you have any recommendations for other resources related to homebrew/low cost lithography?

We use Compugraphics in UK at work for DUV masks (fused quartz 6inch) , base price for 700nm CD is much better than what the sibling comment predicts (sorry but I can't disclose).

Thanks for the recommendation. Do you have any other recommendations for low cost/homebrew lithography?