[stakkur]

Based on my own work experience with such firms, the revenue model is the same as any other contractor/specialist hired to do work--make a margin on every project you can, and keep searching and optimizing for projects that allow a comfortable margin above costs.

The only other model I've seen is to offer a canned solution that's customized for each customer, then charge an initial 'customization' fee and a monthly/yearly maintenance fee.