OP - you could probably fit a Surly CC or LHT fork to your Volpe, and you'd have a "touring" bike for <$100.

A small dent in a main triangle tube doesn't usually dictate retirement of the frame. The dent can be filled with automotive body filler, sanded and painted. All the materials can be found at your local Walmart.

Unless I've overlooked something, your list of touring framesets for <$500 is already complete. Salsa has a couple offerings for $600. BikesDirect has a couple complete bikes for $600-800. Also, there are usually some Novara bikes for sale on Craigslist - unfortunately many sellers are unwilling to deal with the hassle of shipping.

http://www.allofcraigs.com/

http://www.bikesdirect.com/products/road_bikes.htm