What I've seen (though not an official ruling) is that cards with no cost printed on them are assumed to have a cost of 0, and so can be destroyed to get something that costs up to 2. Note that these are costs, not gold values (so the amount of gold you have to pay to get the card in your deck, not the amount of gold the card gives you when it's in your hand and you go to the village).
This is different than my understanding of gold value where I think that something needs to be printed on the card (why else would the Militia cards have a printed 0 gold value? why not just leave the gold value off?) I'm less certain on my interpretations of gold value though, so could be interpreting things incorrectly.