you would need the following:-
a car tyre compressor - £5 from any good car supplies shop like motormania.

a buffertank - eg. a coke bottle, or a coil of pneumatic pipe. Whipper used pipe to great effect.

a valve - available lots of places, including me.

a ram, same as above.
pressure switches.... not really needed if you do it right.

the system can be done for as little as £30.
e-mail me if you need more info, and ill let you know what i have in stock.

Ill have a think about Ewans suggestion of writing a guide unless someone has already done one.