I don't know how your prices are there, but my dealership get about $129 for an ATX Flush.
I flush mine every 10,000 - 15,000 miles now.
Only because I've had problems and had to install an ATX Temp Gauge.
I now flush it when the temp starts to get too hot.
Then after the flush, the temp goes back to normal.

Pete...

98.5 SE Sport Duratec ATX (P66L)
Black Clearcoat on Greystone
DOB 11/21/1997
DOP 12/25/1997
PIAA 510 Super White Driving Lights
SVT CAT-BACK EXHAUST (No Resonator)
DiabloSport Chip (LPQ4) - Engineered To Raise Hell
Too many other mods to list...
Sounds sweet, runs quick...
Crazy Horse Dyno @ 121.4 WHP/129.6 TQ