So i hear that my contact focusses mainly on the disposable pod type of coffee.
Some brief research shows a few local roasteries:
http://www.tate.org.uk/visit/coffee-by-tate
http://federation.coffee/index.html
https://www.pactcoffee.com/about
I would guess its going to be around £65 or so for 3kg at a time, which is probably like 150 coffees. So recommendex donation of 50p per coffee should cover the cost of coffee plus any descaling stuff needed. the only thing to check is that we will get throuh 3kg in a reasonable amount of time.