[ACRep]

Rated at 40 racks an hour, an Auto-Chlor Machine has a 90 second cycle time regardless of design (under counter, pass-thru or corner model) and uses only 1.5 (real world) gallons of water.

You are absolutly correct, 8000 loads is an awful lot of loads for an under-counter machine although it could be done, and with good service the machine would last for quite some time.
The machine we are talking about here is a low-temp pass-thru or corner model not an under-counter.
We have many locations that run 10,000 - 12,000 loads on this same machine in a four week period of time.
Lets assume that this location was only open 10 hours a day that would be an average of 28.6 racks an hour to reach 8000 loads in four weeks.
As this person said "we are a fairly big account" this tells me that the loads I have estimated should be in the area of 6,000-10,000 per 4 week period so I split the difference.
$392.00 in chemical costs for four weeks running 8000 loads is actually a ridiculously low cost for chems (Detergent, Sanitizer and Rinse) on this machine. Granted this is based on an estimate.

I would venture to guess that if you measured (cc's or ml's) the amount of chemicals being dispensed into your machine and worked the math you would find that you are spending more than that. Probably more like 5.5 - 8.0 cents per load.
It's easy to do, if you would like to know how let me know.