Are you going all three days? If so, and if you're staying at a hotel, try and split the cost with a large group of people. At the same time, never buy the food and drinks at conventions because they are almost always overpriced.
As for cosplaying, depending on how much you're willing to spend, it can be really easy or really difficult. Honestly, I've been cosplaying for over 4 years and my cosplays are still simple ones: MTS outfit Domon Kasshu, Travis Touchdown, Hei (BK201), Frank West, and Scott Pilgrim. All of those cosplays I did with pretty much simple clothing, save for Hei, since I bought the jacket.