I often use Air BnB when I travel solo for festivals & cons, as I really just need a quiet place to sleep & washup. I'm not concerned with amenities when I'm going to be out at the event any time I'm not in bed or in the shower. If I can get somebody's spare room with a twin bed for <$40/night, that's that much more money I have to put towards the reason I came. This year I found one close to the #10 bus, so I don't even need to pay for parking at the con. (Sure, a cab fare if I decide to stay out late might might make the parking savings a wash, but if I'm up late I probably shouldn't be driving anyway. ;) )
That's suburbs prices though, so it doesn't make as much sense for someone wanting to do lots of cosplay changes, field big wargame armies, or whatever other things make close hotels a priority. The folks hosting downtown know they've got a high-demand product on a busy weekend, and the prices are considerably higher than what I'm looking for. Still it's worth a look.