That is a tough question as it depends on the contractor. Figure roughly $3000 for a 3/4 bath, then if there needs to be an engress window put in that is around $2000. Now for a guestimate you can use $30/square foot as a guide. Each contractor will have thier own prices. If dealing with a contractor besure you get specifications to go along with the price. AND, get a anthuroized alternation form with a price for every change you do to the origianl proposal.