My M5 is listed for sale and I got a call from Longwood concerning an online ad they will run for me.
The cost is $89.99 and they offer a money back guarantee (less a $10 processing fee) if my car does not sell within 90 days.
I spent $110 to run a classified ad in the LA Times and got exactly zero phone calls in a week, so $90 seems pretty reasonable for 90 days of exposure and a guarantee.