You probably could find a builder who would be prepared to remove the asbestos but it should really be done by a qualified company. I am a plumber by trade but i have seen this done many times, Involves portable showers, full body protection, everything is baged up and disposed of propally. To be honest if it was me i would a few things into account and go from there. Firstly the colour of the asbestos, some asbestos if taken out with care really isnt that dangerous, it only becomes aproblem if it is broken up and all the fibres escape into the air. I believe white is the least dangerous and most common. Secondly the amount, if its only acouple of bag fulls i am sure a local builder would have no problems taking it down, just check he is disposing of it correctly. You dont want the local kiddies playing swords with it down the local fly tipping site. Being in the trade i would say the best and cheapest way to go about this would be to contact some local rubbish removal companies, always in the local papers to come around and remove the garage. This will save on your skips as they usually drive tip up lorries. Then get your builders in to quote when the site is clear.