For those headed to the Galapagos you'll probably be using Puerto Ayora on Santa Cruz Island as a starting point.
There is an awesome night market where you can get grilled spiny lobster for all of $20-30 USD depending on size and your ability to negotiate a good deal.
Up the street north of the port, there is a little fish market where we saw some fishermen selling there catch. There was 1 vendor selling tuna croquettes at $1 each. Great stuff. Highly recommend.