First: If you have BP 1.5.3.1 activated in a WP 3.3.1 installation, best practice is to only add plugins which are compatible with at least BP 1.5 or WP 3.3. If you install plugins compatible with lower versions of BP, be assured in all probability, you’d get fatal errors somewhere.
If you mean a single ning site (not the whole ning), it could cost you $4000 – $5000 to set up. Could be higher depending on your requirements. That doesn’t include maintenance, upgrade or server costs. Of course, could be cheaper with other devs. You could post at http://buddypress.org/community/groups/bp-jobs-board/home/ and/or http://jobs.wordpress.net/