Monetizing Automated Testing?

My company is an IT provider for several large websites. Before a typical release, we test all scenarios by hand. It usually takes a couple hours which are then billed to the client.

We're discussing the idea of moving to mostly automated testing before releases. While this is a big efficiency gain -- 3 hours turns into about 30 minutes -- this is still 2 and a half billable hours which we lose.

The advantages of automated testing are substantial for our clients, but don't justify a 6x rise in prices.

Is there an alternative approach that anyone is familiar with that utilizes automated testing for a unique revenue stream? We've been kicking around ideas, but have hit a brick wall in terms of losing billable hours.