In terms of places to get estimates, I would start here or here or, for a more interesting alternative, here.
Also, it's worth noting that there is currently an interest free loan available for cycling infrastructure, including shelters and racks. It's available from Energy Saving Trust, and I would recommend contacting them directly to find out more. I have spoken to the assistant manager of Scottish Transport within EST who said he is more than happy for people considering the loan to contact him directly. His name is Stephen Rennie and he can be reached on 0131 555 7874. If he sends me more information I will post it up here.