You're being intentionally obtuse here. You didn't prove anywhere that this was the market price, on the contrary, there are good reasons to believe it wasn't.
Traditional way corruption works in my country is exactly that: the people who purchase goods using public money make a deal with the vendors, behind close doors: "I'll buy directly from you, and you can inflate your prices, but you kick back 25% to me". So the seller doubles the price, knowing they have no competition, pays 25% in kickbacks, keeps a nice markup (still sold the item 50% more expensive than they would otherwise). An accountant would find absolutely no fault anywhere: there's purchase orders, invoices, receipts, everything matches. They have no idea how much sprayers cost or how much a specific model should cost! An auditor, on the other hand, could ask exactly these sorts of questions (why was this a direct acquisition and not a public auction? what was the benefit of selecting this vendor? why can I find this model available at 1/10th of the price at a reputable retailer?)
[edit] Look, I actually agree with your take (what this auditor is doing is sketchy, he is certainly not taking on "the establishment" with his saga, his motives look dubious). But that doesn't make the supervisors innocent. He can be shady, supervisors can be shady - these things are not mutually exclusive. For the life of me I don't understand why you defend the supervisors, contradicting yourself in the process[+] instead of focusing on your actual valid point. Yeah, he should get his auditor position; no, he's not fighting the establishment, he's just trying to gain popularity by creating outrage.
[+] first say "find me one suspicious line item" then after several are found, you change the subject or try to pedal theoretically-possible-but-highly-improbable theories ("we can't be 100% certain the price was inflated! What if you found a similar thing at 1/10th of a price, surely that tiny town needed a premium sprayer that had to be very expensive").