I throw in my take. To make it easy, I'm referring to Archive of Nethys for my discussion, at (AoN Formula page) . It looks like the only cost associated with Formulas is buying them from an NPC. There is no discussion of a price associated with the activity of copying the formula into your formula book. (This also does not destroy or expend the formula).
I think a useful analogy is a schematic for Plate Mail, a level 2 item with the understanding that an alchemy formula should be treated the same way. If one player found the schematic for Plate Mail in treasure on an adventure (say from an abandoned Fort Smithy). Multiple players (with formula books) could copy that same schematic into their own Formula Books.
So, what does it take to actually copy the formula? The only thing the next specifically states is time. (Presumably you need something to write with and something to write on.)
If a player decided to spend down time making dozens of copies and spread then across the land, all that's spent is time and writing supplies.
Edit: ah, but what about the rules for Crafting Items: (AoN Crafting Skill page)
Is copying a formula Crafting an Item? I think that it is not, because a) crafting an item needs a formula, and there is no formula for a formula scroll and b) the Craft skill gives a completely separate time rule (4 days) from the copy formula rule (1 hour). In fact the rules for reverse engineering a formula are more like crafting.
Just to reiterate: this is my opinion.