Tool to be used on a car that's how expensive? For how many years?
It'd be an investment, and you can certainly get by with just the tool and a single wideband though. If you forsee messing with carbs for a while, it's not a bad way to go.
Have some friends run O2 bungs in their cars and split the cost, rent it to them, etc.
I usually find a way to make specialty tools pay for themselves
and you also have local friends who are into cars! My best friend drives a Range Rover or his wifes car - an Infiniti G37S.. my other close friend drives a Focus.. LOL