Just my humble opinion
I would pay an hourly rate, with targets and bonuses.
Structured scheme - as I said the product that you are selling is not enough high value to be comm only. However if based around a certain amount of new business - you have to offer an incentive as in all sales jobs, otherwise no motivation to do well.
Im no expert in this industry with regards to conversion rates, and how many calls you would have to make to get a booking, you can only judge this if you have done the cold calling yourself.
You could for example, X amount of new business £15, and so forth. (thats just a speculative bonus)
Heres a site thats looking for people, however I dont think that they will have much luck with comm only
http://www.peopleperhour.com/