Customer Self Service
Achieving significant revenue at a low price point naturally entails driving complexity and cost out of the purchase to clear the floodgates for high volume.

Transactional Sales
As price increases, customers become less willing to part with their cash without at least knowing there are actual trustworthy human beings behind your website URL.

Enterprise Sales
While most SaaS startups gravitate toward transactional sales or customer self-service, some SaaS startups have products that provide so much value per customer and are so complex to buy that their natural starting point is traditional enterprise sales.

(via SaaS Startup Strategy | Three SaaS Sales Models)