This TBT shop thread sells "gardening items" for 5 BTB each (including hybrids). The shop seems to be fairly popular, so it is safe to assume that people find the shop's prices reasonable.
This thread on the TBT Marketplace has someone selling hybrids for 3 BTB each, but it is also of note that the seller is "hoping to sell... quickly as [the items] take up too much space." It is then safe to assume that they are willing to go a bit below average market price in order to get rid of the items more quickly.
This TBT Marketplace thread, as well, has someone selling hybrids for 3 BTB each. However, they do also say the following: "I have way too much stuff so I'm just selling it all." This implies that they are also willing to sacrifice a bit of profit in order to get rid of the items more quickly.
NOTE: That thread has a status indicator in its title (it is currently "OFFLINE"), so the title may change by the time you get to it (and then the link would not work, I think). Just in case you may need this information: the thread is by user Goldenapple and the title (as of now) is "| Hybrids & Unorderables | Status:[OFFLINE]"
Of course, the discrepancy could also be attributed to the fact that large shops that have an established place in the TBT Marketplace are able to charge slightly more because they are known for providing fast and reliable service.
I also just found
this TBT Marketplace thread (also with a status indicator in the title -- which is currently "ஐﻬ Some items ஐﻬ Gardening ஐﻬ Sets [OFFLINE]" -- and the thread was created by user Witch) which has hybrids for sale at 2 BTB each. (Gold roses are 3 BTB each, however.)
I guess, then, that the average is about 2-5 BTB per hybrid!! The amount you can charge per hybrid probably depends heavily on the context in which the hybrids are being sold (in a "store" or a stand-alone thread, in a bulk order or just one or two hybrids by themselves, etc.)
I apologize for not being able to find a single particular thread that has this sort of information! That would probably be a good idea, though. I know there's a thread like that for the tracking of the going prices of collectibles. (
This thread.)