Classified section does not really need any new addons, it just needs some finetuning with basic Xenforo functionality already built in. - make thread prefixes clickable so any user can only look at just the for sale ads or just buy ads or just trade ads. - force users to always select a prefix...
I was in the same position for quite some time, ended up with a .25 cal Reximex Throne Gen 2 and I am really happy with it. Very high quality stuff and prices seem to be still competitive, hopefully they stay that way from now on too.