I've just ordered the bits and bobs i need to make a DIY unit (two 2 litre bottles):
Airline - 60p
T-connector - 30p
Non-return valve - £1. 98
Aquarium silicone sealant - £2.99
= £5.87... bargain. :D
Edit: Bugger, i forgot to order an air stone as well. :fun: I knew there was something i'd...