Sorry but you can't mix 1g with 2g. All members of a port-channel must be the same speed. See the output of command "show port-channel compatibility-parameters" for more detail.
Now lets say you have 5 x 2gbps links in a port-channel. The bandwidth sum will be 10gbps. The cost for a a 1gbps link is 1000, so therefore the cost for a 10gbps port-channel will be one tenth of 1000, ie cost=100.
