I run forest fungi. Making petris takes time and effort, and maintaining a culture bank can be tricky. I give students 50% off, and usually give multiple petris. I also only sell cultures that I have tested. Overseas some of these cultures are $400+. I regularly trade cultures. I have a bank of 20 plus cultures, but only grow a few species for myself and chefs. If someone wants a rarely used culture, I have to make a batch of petris, inoculate them, incubate them, and then choose the best ones to post. All my cultures I send are fresh, not frozen. I used to do it for free, as do others here (watertrade got me started), but I can't afford to be a charity, so I charge enough to make it worth my while. I also don't place restrictions on what you do with my cultures...others have bought my cultures, then started selling them with restrictions on what you can do with them, and renaming them as fictitious species...