If you can tacle dev issues (PHP mainly) and of course HTML, there is Dolphin by Boonex.
The free version is limited, but the paid package is awesome.
It's really a professionnal script intended for any kind of social network. Possibilities are endless.
Of course, there are other scripts similar to Dolphin, but it's the one I picked. However, some new tools might have come up since I did my selection.
This solution doesn't solve the price issue, but I strongly recommended getting out of web stuff you don't have total control over.
It's a basic principle in any ambitious Web project. On that one, you can trust my experience as a Web consultant since 2003.
Ning is a prime example of what happens when you don't do it right. Only thing you did from the start is build up value onto Ning's business, but now they stab you in the back and there is nothing you can do about it.
Choosing another external ressource like Ning is the easy and cheap way, but it's not the right way (if you are serious about the community).