Bump Rate Limiter - keep people from bump-flooding

[styleforum]

We have a busy sales forum and we're struggling with the bump policy. Some people can sit all day and bump every 20 minutes thus pushing everyone else's items/threads down quickly. We've instituted a "no free bump" rule where we require a significant price drop, but that means people work around it by answering questions in their thread, posting "X Sold pending payment" etc. which all bump the thread.

I'd like something that, within that forum only, would:

-allow only the OP to reply to the thread
-lock the thread for replies, for X hours from first post time, hopefully while allowing OP to edit the first post
-unlock after X hours to allow OP to bump, then relock thread for X hours again
-repeat.

This would keep people from bumping threads more than every X hours, in our case probably 48 hours.

Is something like this available already? If not, is there something that could be adapted?

Thanks.