Open Source VDI
I am not trying to be a Microsoft evangelist here, but I think that you are not looking at the whole solution. You state that using a Microsoft server solution is expensive, well it can be but Microsoft does have massive discounts on licensing for registered charities. Also have you thought about the total cost of ownership? Many of the Open source solutions are free to install but to get support or upgrades can cost much more. Have you thought about after care with getting either full time employees or consultants, they will cost more than a windows admin or support will cost. I am not saying that Open Source is bad or that it does not have its place in solutions, because it does. Sometimes it is better to invest in a common technology for the long term which will keep both support costs down and the end users comfortable in using industry standard desktops or kit.
As a disclaimer I do IT Management consultancy for Charities and Retail organizations.
If you need any assistance please feel free to contact me www.tugboat-tek.com
Biting the hand that feeds IT
