All of the companies give good deals for a few months for new customers as an introductory price. After that they all go up to the ridiculous price.
Just move your current Comcast account when you move. Remind them that there are better deals in the neighborhood, and remind them again every year or two. The customer service rep will almost always give you a little break and cut your rates for a few months; sometimes six months or more.
There are some places you can check to see if there are better rates in your new area.
For example, here are a couple I posted for someone else who was looking:http://www.dslreports.com/searchhttp://www.myispfinder.org/