i do my own fluid flushes now with a Motive Pressure Bleeder (google it). otherwise a typical flush at a shop should cost no more than $60+fluid...
you can get one bottle of ATE blue for about $13-15 online. order it and get it shipped to your house then bring the fluid to a shop. you only have to do this once per season if you dont track too much.
i do about 10 track days per season and flush my fluid twice a season.
Current: 2013 F10 M5 & 2013 GLK350
997.1 GT3RS (gone)
2009 WRX STI (gone)
e92 M3 (gone)