A wiesco kit and factory KTM parts arent any where close in cost.
https://www.rockymountainatvmc.com/oem-schematic/0
Personally I like OEM pistons but each their own opinion.
So lets say this guy has $400 in parts
Piston kit
Gaskets
Oils
Plug
Valve shims
And then lets say he has 10 hours in labor at $65 an hour ( common for a bike shop ) for cleaning the bike up good enough to take the top end off, taking the bike apart, cleaning all the parts, oil passages and going over the head and valves. Putting it back together. Now take into consideration this is not just a slap it together back yard job, its a professional job doing everything right. That takes more time.
That brings us to $1050, now add in profit of $150. After all that is why people are in business, to make money. Remember, as a business he has overhead costs to pay....utilities, shop supplies, insurance, postage, fuel, taxes and paying himself and any help. Honestly I wouldnt do all that for $150 bucks. It barely covers his cost. If you want it cheap then learn to do it yourself.
Now does that seem a little more reasonable?
However, a good attitude goes a long way. I think the shop owner could use a little better public image. And I am using assumptions about his business and its needs.