That's about a $15.00 or $20.00 for a shop.

On a 7 or 8 speed I can usually align it adequately by eye to get the shifting to index correctly. 9-speed cassettes and above are spaced so closely that I need the proper gauge to set the alignment. I clamp a big crescent wrench over the derailleur. It's good to keep something screwed into the derailleur mounting hole to keep from ovalizing the hole.