Development environment - Speed issue due to VPN and client

Question

The issue is that we are developing a system which is heavily dependent on CRM located on clients network and hence we have to work over VPN and call web services ( CRM SDK API's) to access the CRM repositories. 

 

We are loosing 30-40% or more on development productivity as its gets very slow due to VPN latency and CRM response.

We can not have a local CRM environment but getting sample data wouldnt be much issue.

 

 I am wondering if anyone can suggest anything that can help us create a local environment which would be similar to CRM but can be either fake repository or a local instance of Sql server but in this case we will need similar web services so integration would be CRM at the end is seemless. 

 

Hope i explained the situation. Thanks in advance.

Vishal