I think a reasonable approach to sell would be try to convince the buyers that your QA-as-a-Service would replace QA employees for a fraction of their cost. Thus, pricing would be a fraction of the cost of these employees. I think it's a good idea. Btw, you can pretty much validate it entirely before getting started: just approach companies with mid-large QA teams and try to convince them of the value prop (high-quality QA at a fraction of the cost).