I paid the shop around that amount for the gear and the replacement on delivery of my new DS a few months ago. The replacement is straight-forward, of course, but can become complex very quickly. The shop had to remove the motor and heat the shaft to pull off the stock drive sprocket. Pressing on the new 25T drive sprocket is not as difficult, but requires proper torquing, etc. The removal process probably damages most sprockets, as it did mine, but they are low a cost item.
My speedo is off by ~10%, or so (haven't checked against the radar signs), and I understand the shop can reprogram the unit, although mine did not do so during the installation and upon request. I don't miss the reduction in top-end, or max sustainable speed and do enjoy the slow-speed torque, although I have only ridden 5 miles with the original gear and am not experienced enough to compare the torque-performance differential.