i'm from CA too and interviewed on campus. paid something like $500 for a RT ticket from SFO to ITH. got a hotel on hotwire for $65/night (the 3 star one is Holiday Inn and they have a free shuttle that will drive you between airport, hotel, and campus). I was in and out of Ithaca within 24 hours.
if Johnson is high on your list, pay the money and do an on campus interview. although the official party line is all interviews are weighted equally, if you get waitlisted (or worse), you don't want to wonder whether interviewing on campus would have made a difference. when i interviewed on campus, 75% of the other interviewees there had flown in from outside the US. if others can fly in from Shanghai to interview, you can fly from CA.
Sylverlee
R3 just got emailed for an interview invitation. w00t. $640 just for the plane ticket out there from Cali ouch! Do you guys usually just fly there, interview, sleep, and then go home?
I also was coming from California. I went and was accepted (R2). I know it is pricey, but with a school like Johnson I think it makes a big difference. But, that being said all interviews are supposed to be weighted equally. So, I think the biggest decision factor is if you want to see the campus and see if it is a place where you could see yourself. I went in on a Saturday for my Monday interview so I wasn't too tired or anything. Also, it gave me a chance to see Ithaca, which was important for me. If you haven't visited, I would recommend going if you can afford it and take the time off.
As for cheaper flights, I paid under $400. I used hipmunk.com to help me find better deals. I love that site! I've found it is so much easier to use than other sites.