If you adjust for inflation say since 1999, raising your 19.99 price to 24.95 is about right. That's just the inflation angle. I also think you have to consider the time and effort and overall resources it takes to make a sale now verses that effort in 1999, it would probably be substantially more. Time is money spent.

The affiliate angle also has to be part of the equation. I agree that half of 29.95 is very appealing. I can think of only a few sites that could sell that price point well.