I tend to agree with MickyWall.
Have you installed Google Analytics on your website also? This is really important because you will see keyword variations. You might find that yes, you are bidding on the word "kitchens" but you are actually getting your best traffic from the keyword "kitchen renovations" or "kitchen specialist".
Kitchens is expensive as you say, but you can cut costs significantly and find all kinds of valuable data by looking at Analytics.
I just wrote a post tonight about setting goals using web analytics that may help.
Tracking Goals with Web / Google Analytics, Why Its Important! | Gavin Doolan
If its a bit much all at once I apologise, but feel free to ask questions. I'm happy to help out.
Oh and if you could send us a link to your site, we would appreciate it.