There's no single answer. But like other specialized services its usually flat-rated and subjective to location. Around the GOM area its $300-$500 for single/twin private recip aircraft. Higher for business class/turbine/helicopters. Other variables can be if you travel, type of equipment used, rental equipment or own, or if your service is standalone or done as part of larger work. Perhaps look to see who offers weighing services in a 100-mile radius from your shop and see how you would fit in. But its kind of like prop balancing services, unless you can justify the equipment cost vs usage, you tend to end up paying more for recurrent calibration costs than it can worth in the long run.