The maintenance schedule for the 2006 RAV4 says to "inspect" the transmission fluid every 30k miles. If the RAV4 uses Dexron II transmission fluid (check the owner's manual), it should be red in color. As you put on the miles, the fluid gets dirty and takes on a brownish appearance. If all they want to do is drain the transmission and replace the fluid, the cost should run only a little higher than an oil change (transmission fluid is more expensive than oil, and there's a little more labor). However, most transmission service usually requires that the transmission pan be removed so that the transmission filter can be replaced. $155 for that service doesn't sound out of line.
Its possible for transmission fluid to need replacing at 30k, depending on how the car was used. Heavy duty use (pulling a trailer, off road activity, stop and go traffic, etc). could accelerate the deterioration of the fluid.