I work for Lakeside Service Company of Brighton Michigan. We (I) do duct cleanings and I would be happy to give you some insight. I am not familiar with other companies, but we use a very large abatement technolgies portable vacuum inside your home and connect it to your duct work on both your supply and return trunk. It is best to split the system into 2 parts, return and supply, you will double your suction that way. We have a large truck mounted air compressor and we feed air lines into each vent. The whole process on a typical home would take around 6-8 hours with one person, if the company you chose gets out in 3, then I would question how well they cleaned your duct work.
Our pricing begins with a base price of $450 for the first 15 vents, $10 more for each additional vent. I believe we also have a $50 coupon also that I usually give out. I have never traveled that far for a duct cleaning, so I dont know if my boss would like me to offer any services that far, but if you would be interested I am sure we could work with you, or I can atleast help with any questions regarding other companies.
-Joe