From what i have read, your saying you have created a system in which it makes it faster and easier to create these sites for your customer, and your worried about loosing out on other business.

Cutting prices for such a client in my eyes would do nothing but be good business sense to continue with. Not only will you be recommended for your services, but your going to be completing the work with this client quicker... your not really taking a pay cut, because you wont be working on the site for as long.

You'll will get a reputation for great customer service, and should pickup more work - Where you can gradually bump up prices. Stay loyal to loyal customers.

Good Luck!