These two places offer training in a twin seabee:
www.ryanseaplanes.com/ in Florida;
http://seaplane.hypermart.net/multi.html in Arizona.
The first place quotes an average total cost of between $1,800 - $2,500; the second outfit charges $325 per hour dual.
Training in a Grumman Widgeon is also available in Florida:
http://www.geocities.com/flseaplanes/ Probably more fun than the seabee, but the price is $420 per hour.
Hope this helps,
MLS-12D