The cost should decrease substantially over the next couple of years.
Walmart's movement to RFID, and subsequent requirements for it's distributors to do the same will popularize it the same way they got UPC codes accepted 20 years ago
Major tire manufacturers are putting them in tires as well in order to track inventory. Imagine linking that system to a toll road? Your tires would would act as the transponder on the 407 :P
Though the cost of the chips is about 5 bucks US now, it's expected that they will drop to a nickel each before the end of the decade