I use to define my top price as well, but I preffer to bid on it 1 minute before the auction ends, or so. That gives me a bit more chances.
I was once hunting for MONTHS an SX64 on eBay, once I put 200 dollars on one and I got outbid. One day I saw ne and, without much expectations to win it, I threw 160 at the max price. I won it for 80!