self-reply: I ended up just calling Spirit's fine call center in Bangalore to take care of this (the English-accent training went well, but maybe a little Spanish language training might help too...Medellin sounded like meddlin'!) Anyhow, they said their website did have a problem and so they could book over the phone without the fee. It took FOREVER to get the details out, but 25 later I am now booked and flying to Medellin from Boston for 180 bucks next week. AWESOME.