The least expensive added sales service you can get is a meeting booking service. I am thinking that if you just get someone to book online meetings for you then you yourself would be the best person to actually close a deal with the client.
The cold calling / market prospecting work is very time-consuming and you need to get someone else to do this so you can focus on the last half of the sales process.
Meeting booking services are normally not commission based but rather a fixed fee per meeting booked (or per month), but fees can be quite low.
I run such a company myself so contact me if you're interested.