I had my Hunter 29.5 converted to electric propulsion last year. It could be a DYI project if you're very comfortable with wiring your boat. Looking at my costs, you're still looking at another $3-5k for batteries, controllers, and supplies; if you do your own work. A great place for more info is:
Electric Seas - A Resource For The Electric Boating Community
. This site is dedicated to electronically propelled boats.