I'm a private English-Chinese interpreter in China. People often send Email to me to ask my rate. As soon as I tell them my rate, they often don't contact me any more. I don't think my rate is very high given my expertise in this field. The problem, how I can deal with the price/cost inquiry tactfully?
To build upon what others have said, show them the value you deliver. Including testimonials from previous customers is often effective in doing so.
Send them your rate with a direct link to a portfolio or reference.
You could say that your rate depends on the subject, deadline, complexity,... But above all, show them that you are worth your rate. Your message should be: hey, I understand my rate is a bit high, but if you want a quality product, you have to pay for it.
Play on your customer's fears also, reminding them what their own customers may think if they give them a poor quality product.