I blew my own insulation in with the help of my wife. I had 4-5 inches of insulation when I started. After blowing 40 bundles in I had about 30 inches of insulation. I used cellulose. Total cost was $200 because I had coupons. Without coupons it would be $300. My house is 1500 square feet for reference. It only took me 1 hour of time.

Questions I would ask for those giving you bids:
Approximately how many hours are you planning?
How many employees would be working during this time?
How many inches of insulation will be there when complete?

If you have 1500 square feet and they are adding 24 inches it would be $300 for the materials. Add about $25/hour for each employee they state.

For 2 employees taking 2 hours and approximately $300 in materials
Anywhere near $500 would be a reasonable quote to me.

We plan to put insulation in our attic when it cools down again next fall. We are going to use the spray type. Our attic has insulation, it got wet when the roof blew off in Ike then melted when the roofers set the house on fire. No telling what kind of mess is up there, the guys just worked around it when the house was repaired. Instead of trying to get out that old nasty stuff we are just covering it up. I don`t even want to think about it. I`ll probably pay my brother,he`s a contractor, to do the work.
Tally HO!

wait, we have balloon framing so no spray on insulation, it just falls down between the walls to the ground. Drats, forgot that.
Tally HO!