What would an open source fab be like? Even if you had the space, all the stuff that goes into making a chip is highly proprietary (chip simulation/testing, equipment, chemicals, plastics, ventilation etc) - some company spent a fortune building it and they want their cut.
The next best thing - companies like TSMC will take your design and make a chip - it's not even that expensive (as far as making chips goes) - they publish all the manufacturing guidelines and everything so there's no pre-flight issues (can your chip actually be made with the equipment at hand).
Another process is (that involves proprietary hardware again) - you can buy a pretty nice FPGA, design it, test it - and hand that off to be turned into a real chip.
I think it goes without saying that chip making is still one of the most sophisticated manufacturing processes in the world still, but it's not hard to have your own open source design become a real chip. Granted - you may spend 140k on a batch of a thousand chips that don't work (or don't work right), but that is part of the process.