That's just nuts. The last time I had my reg serviced it cost half that and it still drove me to learn how to do it myself
I was curious about how badly you were getting gouged by the shop so I looked at a place that's known for reasonable mail-in pricing. It turns out most of the gouging is from Atomic which has what the Brits would call "taking the piss" prices on its service kits.
~snip~
The second stage kits are a little more reasonable, but it's almost $130 just for the kits. You could find cheaper labor elsewhere, but add in shipping in both directions and the cost for the convenience of an LDS is pretty small.