"How much does it cost?"
In a previous post I used a restaurant analogy for the time a project takes to complete, and it's also pretty apt here. If a menu had no prices, I'd be sceptical about ordering.
Not only sceptical, I'd probably be nervous. Although JP Morgan's famous quote "If you have to ask how much it costs, you can't afford it" is pretty condescending, not many people want to feel inferior and out of their depth.
So to avoid making potential clients feel that way, list your prices.
If they vary, at least give a starting point. Be honest and show your clients the respect they deserve.
Showing your prices shows that you know what you're doing and you know how much your work is worth. This also gives clients a decent idea of how good their return on investment is likely to be.
If you pay $2 for a pair of shoes, you're unlikely to expect the quality of a pair for $200. Expect the same for everything.