Many people have done this in this community. The process typically involves using a Wordpress utility to export all WP entries and format them into a Moveable Type format (single file) and then using the MT import utility to bring those entries into EE.
The MT import utility for EE works nicely but the WP to MT export utilities are created by the WP community and the quality of these scripts widely varies. There are a number of them in the wild and you will just have to Google for them.
There are other details which largely depend on exact needs of your WP installation. Some WP site are more complex than others and this would influence the price. There is no standard cost or time estimate and the numbers are likely to vary wildly depending on where you get an estimate from.
You may want to post an entry in the jobs section of this forum. Or look through the pro network.