It's difficult to put a posted price on an investment like this because there are so many options to choose from and variables that that will affect the price.

A. You might just want the number routed with no web access features and no other number.
B. You may want to cancel your current "Who's Calling" type of service and get 20 or 30 other numbers along with a memorable, powerful number and save a lot of money from your current provider.
C. You may want to get the number nationwide or corner the market on a major city, on a permanent basis to get branded.

Call your representative directly for details.