Speedbird744,
I wouldn't place too much reliance on a TCAS system - even one that's not cheap relies on the other aircraft having a transponder which is switched on at the time.
A lot of aircraft don't have transponders. Having flown quite a bit around SE England with a TCAS-equipped aircraft recently I'm surprised at how many which presumably do have transponders don't seem to switch them on.
TCAS certainly can help, but since you only have to hit one aircraft in order to spoil your day you can't afford look out any less than you would otherwise do.
What TCAS does help with is telling you there's something out there that you hadn't spotted even when you have been looking. That happens alarmingly often.