"How much is the scan tool that connects to VIDA?"

The VCT 2000 which is what Volvo dealers use to go between the PC and car, has the OBD2 plug costs the dealer ~$2,000 US.

A subscription to VIDA costs a dealer about $600 per year, per PC not including whatever they'd charge an individual to purchase the SW itself.

Volvo has made all this so costly that few independants would ever consider buying it. No small shop or individual would do that, no real need.

If you think about it, unless your car is an electronic nightmare like the '99 S80 (for example) which has many issues often, you're still probably not going to ever spend that much money taking your newer Volvo to a dealer when VIDA is required.
Even IF your car was a '99 S80 and you had VIDA plus all the electronics at home, could YOU or anyone else w/o modern day Volvo training, experience still fix the car? Vadis and VIDA is not so great that it tells the user exactly what's required to fix the car. That still usually takes further diagnostics and mostly, experience.