The general rule of thumb is 11.5 as a target AFR for turbo/supercharged cars.

You can start there and work around it if you had too. Some vehicles require a 11.0 to run problem free and some can go leaner to 11.8 or whatever and still be fine.

Any of the gauges that most of us buy are $150-200 dollars. I've ran two AEM gauges and hard no complaints. Innovate LC1 is a gauge, autometer makes one.