$100/tank for service is crazy. I bought a new alu80 for $100 from Sport Chalet. LeisurePro.com lists an alu80 for $125.
Here's what the following services involve (+/- a little depending on shop):
VIS: Check tank numbers for expired exemptions, remove valve, remove stickers, look at outside of tank, look at threads, look inside tank, use pick set to check depth of pitting, look at valve, reinstall valve, sticker. Time is about 10-15 minutes, one time purchase of tools is $100-$200 (more for eddy current tester used in VIS+).
Tumble: If rust or corrosion is found in the tank, put it on the tumbler, add the tumbling media, turn on machine, ignore for a while, pour media out, clean inside of tank, then must do vis. Operator time: 20-30 minutes, one time purchase of tools $100-$500.
Hydro: I take tanks to a dedicated hyrdo facility - cost is $10-$20.
Cost of a brand new valve to replace one you don't want to clean up/service: $10-$40.
It's reasonable for a shop to be paid well for their time, and to make a markup on parts. $100/tank sounds unfair to me.
Note: While I am certified by PSI to inspect tanks, I don't do alot of it and the above is from memory. Please don't roast me too badly if I've left out a step. I don't think anyone will disagree too strongly with the time and tool expense listed above. If anything I exagerated the service time.