Customize White-Label Social Network Program (e.g SocialGo, Ning, BusinessSpace)

I am looking to customize any one of a existing white-label Social Networking products. It is however not for a 'niche' market which only needs tweaking to form look/feel, rather I want to customize some core components, mainly registration, group creation, networking between users. Originally I had spec'd out for my own custom site but the cost was prohibitive, and since 90% of what i need exists in these white-label solutions I figure why pay to reinvent the parts of the wheel I am not changing much. I would need a coder/team that has experience with these and can? a) recommend the solution that would work best for my needs in terms of the extensibility of the solution b) estimate the modifications for each module as needed pretty accurately c) has experience with databases, auto-suggest, etc. as most of what we are doing is connecting the white-label back to my db. This would probably end up being a long term project as I'd be modifying/adding modules as we go along, with the first step being registration. Again my key here is to avoid the 1,500+ hours I've been bid to build this from scratch and just concentrate on the implementing the modifications/additions I need.