I found FCP4 on Craigslist for $100. Since I have limited income, I am trying to decide if I should get the FCS3 upgrade now ($359CDN) or wait for the supposed 3.5 upgrade? I am shooting AVCHD and this is all for personal use at present.

Edit: I am on a Mac Pro 2006 (bought April 2007) Quad 2.66Ghz, 3GB RAM, ATI 1900XT 512MB, 250GB Boot drive, 20" Apple Cinema Display (it was my moms bought August 2006), Firewire iSight (bought for my moms MDD G4 December 2003, mine from Oct 2003 is dead).

would you have to pay again for a 3.5 upgrade after already buying 3.0?

Considering the lackluster "update" to the Macbook Pro lineup it's unclear if the next iteration of FCS will indeed include everything the NLE community has been most-requesting for Apple to give us. At the moment I'm not very hopeful it will be worth the wait.

FCS "3" is a superb platform; there's nothing you can't get done with it and, there's no telling what goofy new requirements Apple with post with the next iteration of FCS so I'd say get what's currently available and don't blink an eye.