Typically you would only be able to sell your collections to people who regularly read and enjoy your comics. If you are publishing a paid collection without a free collection first, you're unlikely to sell any if your web comic is family-friendly - not sure how well the adult-only section of this site does - I have the blocks ticked to never see any of it.
Else try Smashwords. They do have people there that will read books / comics etc. You can also browse their catalogues and get an idea of the price. They also have regular sales where you can discount your books up to 100% off.
I remember reading a comic artist’s post on his comic’s reception on itch; the situation was a bit different (namely the comic was free and LGBT NSFW content) but the post may be an interesting read for you, since they share and go into details on a lot of data on how it was received, which seems to be what you’re looking for.
