You should be able to pick one up cheaper than the example you have e.g. eBay.co.uk: 2kg Co2 Fire Extinguisher (item 230092161242 end time 21-Feb-07 09:10:45 GMT). If your regulator is a standard fitting then it will screw straight on in place of the horn. I think you have previously posted that you have a jbl reg, i'm guessing it will be a standard fitting but with a large international company such as jbl they may have their own standard so i would definitely check.

I personally use this regulator http://pixi.aquaristic.net/aquarium/... .html?lang=1 and an extinguisher with no problems. I have just screwed on the regulator and cable tied the extinguisher handle down. PLEASE NOTE: I am not necessarily saying this is a good idea, entirely safe or recommended although I know it is quite a common practice in the UK especially among reef keepers with their calcium reactors.

Cheers
Neil