Sysadmin, proxy solution for bypass geo blocking

We need to setup a solution for providing access for end-users to geo blocked sites through proxy or VPN.

We need an experienced sysadmin to help us with the following:

* Provide initial consultancy on a preferable solution to choose, and make recommendations of which software to use.

* Optionally assist with parts of or complete setup of backend solution (No web GUI coding needed)

* Optionally provide further support/consultancy later on.

Please be sure to provide examples of previous work on similar/related projects to demonstrate proficiency

Requirements for the solution:

* Open source software is preferred

* Lightweight and portable. Easy to setup on a standard Linux server, easy to setup on a VPS.

* Scalable as user base increases (to hundreds of thousands of users)

* User friendliness for end-user. Must provide simple setup for non technical end-users

* Authentication in some way. Either through browser, or by logging in to separate web GUI that adds/writes the users IP to a whitelist/config file.

* Keeping bandwidth usage low. If possible minimize the content that has to pass through the service.