You don't have to go to the Lock-In to play in the tournament. Moreover, it's 10 bucks because it costs money to host games. You know? Electricity and shit? Other than that, yes, 10 bucks to the host and then you just pay money toward the pot for winning.
It's a card shop with a bunch of televisions and set ups (IE: Consoles and games) provided for fighting games. You can also bring your own console and set up and run what you want if you feel so inclined. There are PS3s and 360s at the venue.
Yes, kids, tournaments cost money.