Wow, very nice of you and that is a big cash prize. I'd be happy to help advertise when I'm on more but the last tourney I did, I advertised for 2 weeks and it seemed that it did very very little (somehow). So, I'll help the week of, in terms of in channel spamming.
Your best bet is to try the FB group and/or msg individual people because no matter how much you spam and even say it in game channels, somehow people will be like "wait what? there was a tourney today?"