This can drive down room costs a lot but can complicate costs for travel. With SDCC travel is more of an issue than most other cons. If you're signing up for a room this late in the year you'll probably end up miles away from the convention center.
When I went to my first con I spent $50.00 for the three day pass. However I spend most of my money on lunch & dinner than anything. Which I have to go to the ATM to get more money.