Richard,

Quality Score - there is a wealth of information out there. If you are doing PPC at any level on Google AdWords, you should make the effort to learn more about it as soon as possible.What I was getting at with the "keyword price will potentially increase" comment pertains to the potential of an increased Quality Score to actually lower your bids or keep them level despite increasing your maximum CPC bids (Quality Score rewards relevant advertisers with higher ad positions at lower CPCs).

As for your budget concerns, there's actually a valid explanation for what you're seeing in AdWords. Google looks at your daily budget as a fluid data point which they use to guage your overall spend throughout the course of a given month. So you set your daily campaign budget to $100, Google assumes that you intend to pay an estimated $3000 for that month. The AdWords system intends to meet that $3000 total throughout the 30 day period and assumes fluctuations in daily spend (both above and below your targeted budget). So, it isn't the system jacking around with you, it is trying to level you out for the month. And if you make knee-jerk budget decisions, this only confuses the AdWords system with potentially negative results.

Thanks for the comment!