You could do it yourself, using some of the suggestions listed here. Put in some gravel or abrasive, and find a way to work the rust out of the tank. The compound you require is available. Check out this link:
http://www.canada-por15.com/merchant...de=TankSealers
http://www.canada-por15.com/por-15-tank-sealer.htm
A simple google search will net you many other companies which sell similar compounds. Try the following search terms: fuel tank repair compound coating
The company I linked to above charges about $90 for a gallon, which would be enough to do both your tanks, with about enough left over to do one more. The second link will answer most of the questions about how to do it.
While Mike's suggestion about the tank in the tank will work, there is something to be said for having two tanks in working condition. In fact, I think the term is "restoration" (Sorry big mike)