Well, you're going to need the corny. Obviously. Then you need a disconnect for the gas in and one for the liquid out.
Norm is by far the cheapest I have seen, currently at £55 for the corny, a pair of disconnect and some 3/8" pipework.
On top of that, you'll need a source of CO2. Here you have a couple of options.
You can go for a big bottle and regulator. Regulators tend to go for £15-20 on ebay. The trick is sourcing the bottles.
Or you can go for the small midget widget bottles with a trigger to fire out the gas.
Then at the other end you'll need a tap to dispense. You can go bargain basement and get a picnic tap (but expect a glass full of froth) or get a proper pub style tap. Something like a Dalex tap.
That's your basic setup. Beyond that, you might want to think of a gas management board to run several cornies. And perhaps a dedicated fridge to keep it all just right.
Oh, and bear in mind the cornies multiply. I must have got a mating pair.
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BB,
Is that a beer engine you're running from a corny? Just quickly, how have you got it rigged up? I assume you don't use gas as the pump "pulls" the beer as opposed to having it "pushed" out.