Andy,
How long have you been in this game? Serious question. The reason I ask is that you say you have just lost your first customer. However long it is, you have done really well in what is a difficult economic climate.
My humble advice is to suggest that you stick with your prices, and not let this one ex-customer make you feel that you are not worth what you charge them. If you have been undercut, he will probably be gone again when winter comes, or he finds he can't make a living, or has to cuts corners.
If you drop your prices, you will no doubt attract more work, which will keep you out on the glass much longer than you need to be. But will you he happy working much harder than you need to?
I used to underprice my work. Never again!
Best wishes,
John