Thanks—that makes the initial scope clearer: your mapped layout, a consistent selling-post template, and manual membership access changes for now. I also misread another participant’s API/webhook suggestion as your preference earlier; thanks for clarifying.
One plan detail matters before estimating: if you mean Discourse’s hosted Free plan, it does not support additional private categories for a paid-members section (official clarification). Are you on that plan, a free trial, or a self-hosted installation?
Could you share your category/layout map, with any member details removed, and the fields a selling post needs? Should those fields be required before posting, or is an editable prefilled template enough? With those details I can assess a viable scope, price and turnaround without assuming an upgrade or automatic membership syncing.