I don't understand. What makes you think marketing agencies and existing SM management companies aren't targeting SMEs and startups? I've met plenty of people (and companies) who do this. I don't see what would set you apart from existing services.
Price point?
there are plenty of services but none of them have a package designed for the minimal need and budget of SMEs and starups. I might be wrong in my understanding and thats the whole point of asking here. :)
Please tell me if I am missing some market intelligence.