I don't lube my switches, personally, but ... *assuming* you get 2,000+ buyers, what is your current understanding of the cost to each buyer for 10mL?
Alternately you could say what your cost to buy the five gallons would be. There are a few folks on the forum who make their living, or at least a supplementary income modding keyboards for folks so it's not entirely out of the realm of possibility.
What you're going to get, is a single container about the size of a paint bucket. Do you have a firm grasp right now of how you'd dole that out in 5mL quantities? How about 200mL tubes that will get through the mail successfully? Also, have you any experience organizing something of this size? You're suggesting somewhere between a thousand, and five thousand folks get together and hand you their cash, and you have to keep track of it long enough to get them their bottle of ooze in as timely a fashion as possible, without mixing up who ordered 10mL with the folks who requested 12mL, and always always always, mailing to the correct address because folks move between ordering, and receiving. The moreso when it's drawn out, as a thing like this will almost have to be.