Hi,
I understand your concern. Let us explain :
Standard IO - Page Blob/Disk (GB) :
This means the total amount of storage you will use per month, and it's calculated per day basis. This is an estimation an cannot be defined by Microsoft because they ignore how much data you will consume. For virtual machines for example, a standard windows
server uses 15 GB, so you can estimate how much Windows OS disks will consume (VMnumber x 15). Ask the customer for the data and application consumption/requirements. Look here to understand how storage pricing is calculated (See the FAQ)
http://azure.microsoft.com/en-us/pricing/details/storage/
Storage transaction
This is the most unpredictable metric, since you you can't define how storage transaction your workloads will make. This can be predicted after months of Azure usage, since you can at least look how 'standard application' behave and how much they generate
transactions in average. But transactions cost will not be important compared to the storage cost itself (cheap)
Basic Gateway Hours
This is easy to predict, since you establish you VPN Gateway, you can calculate its cost (Usually a getaway will be always up and running, and then you will calculate a cost for a month usage). Look here
http://azure.microsoft.com/en-us/pricing/details/vpn-gateway/
You can refer to the pricing section in this blog
https://buildwindows.wordpress.com/2015/05/12/azure-the-virtual-machines-service-introduction/