Brooke used to have a website page about the current financial situation of the patch fund, a kind of general gauge of how close or far the funds are from being able to cover the next patch run. I'm not sure the current rates, and costs do vary from patch design to patch design, but I think it's a little more than a dollar per patch produced including postage for shipping (to deliver that patch).
I'd like to thank those who donate to the fund, as I'm one of the more financially strapped blokes who really appreciates getting a patch for these scenarios and not having to dig through my couch to make it happen.