I’ve found a good online tool that I use for a lot of theoretical “I wonder how much it would cost to…” ideas — Contractors.com offers a free online project cost estimator! Simply click on “cost estimator” plug in your zip code, and select the kind of project you’re dreaming about. In addition to kitchen and bath remodeling (with a range of options, according to budget), they have estimators for outdoor projects, such as driveways, sidewalks, windows, doors, siding, (even garages!), indoor projects, including plumbing, electrical, flooring, insulation, and heating/cooling. They even have estimators for painting, additions, decks, and roofing!
This site also refers you to contractors if you’d like, although I haven’t personally used this part of the service. What’s great is that they let you estimate a project before putting in your contact information — so you’ll only be contacted if you want to be.
For advice on finding a contractor, see this post.