I have paid $50 for 3 pulls and I have paid $80 for 3 pulls. depends on group dyno days vs the shop vs time, etc.
You can tell your horsepower at the wheels thru a dyno. It also measures torque since horsepower is a direct number based on a mathematical equation of (torque*rpm)/5250. If you look, all proper dynos will have the torque and horsepower lines cross at 5250rpms.
Sometimes you can also get your air/fuel ratio printed out as well. That tells you how rich and lean you are running.
All these work in correlation to show if a specific mod added horsepower to your top end or bottom end or all across the power band. The old butt dyno just doesn't cut it for factual data. You can also see how smooth the dynograph is to see if you need tuning because the mod made it jumpy or not.
**I have sigs turned off, so if you're asking for advice based on your mods, I can't see them**