The Polaris tune-up kit (A49) is about $200. The Polaris rebuild kit (A48) is over $300. He's using 3rd party tune-up kit and charging you for 2 hours work. Sounds about right.
If you're at all handy with a screwdriver, the instructions are pretty straightforward - you should be able to do...
^^ What he said. Unless there's some problem with the 280, just run it for a couple of hours a day (ours takes ~1 hour to clean our pool). If these is a problem with it, replace it with another 280 or, better still, a 380.
If the concrete decking is prepared correctly, Kool Deck should not not have any problems. The issue is finding someone who knows how to prepare the decking correctly - a quick high pressure power wash while you're not around ain't gonna cut it. A chemical cleaner followed by an approved PTA...
This is the only way to repair them properly. It'll take you a couple of days and 50 bucks worth of materials. Beats paying some clown $7k or painting them with something that will only last 1 season. Use a gelcoat on top of your patches.
The cloudiness is normal after adding a metal chelator. I wouldn't add too much chlorine yet as the cloudiness may not be algae and it will counter the metal magic treatment.