Its cheaper – so no problems. Put it on your site – when it get’s popular hide it. People like to see whats in store for them – no hidden stuff.

It is not wise to do so. What is important is to show your work as this will being clients to you.

If your rates are significantly cheaper than most, then I would suggest you put the rates on the site.
The main reason websites don’t list their advertising rates is that someone doesn’t undercut them. If their competitors don’t know the prices, it makes it more difficult for them to compete.