I'm not a paying member yet, though I plan to become one very soon (next month? )
I have trouble finding things in the BP classifieds also. It's difficult to sort through the posts--sometimes people ask really good questions on a "for sale" thread where I was just about to ask the same thing to the OP, but it's already been asked and answered on the thread. Other time there's 6 pages of "bumps", and I hate scrolling through all of them just to find the pertinent information, such as the good questions, which animals have been sold, etc.
Most often though if I have an offer I want to make to a seller I just PM them as I don't want everyone on the whole board seeing that. It just takes up space.
I don't know of a solution, but then again, I don't know all of what is capable of being tweaked on an internet forum, and I don't know to what extent it can be tweaked. I'm sure the mods will figure something good out.
(Besides, $25 to become a contributing member isn't bad at ALL,especially not when it goes to a good site like Fauna.)