Niel: $23 from PB Tech. You need to tick the box on the right to get the GST inclusive price. Anyway, cheap.
If you see a Chorus van in your neighbourhood, ask the guy if he is interested in a simple cash job. It really does not take that long to do.
To get it done officially is a standard install which I believe is in the order of $150 to $200. No one cares if it is done officially or not, as long as the splitter is Telepermit approved and you have standard phone or solid core network cable.
Phone wiring is just 2 wires with low voltage on it (or a few pairs of which usually only 1 pair is used). The gel filled cable joiners can be purchased from Jaycar for relatively cheap, or maybe Dick Smith (expensive if still available). You insert 2 wires into the gel cavities and whack it with a hammer to drive a blade through the insulation to make the connection. Just keep the correct polarity.
Sorry but the reason the install is so much is that the splitters chorus use(who i work for) cost us around $90 (dont quote me on price) and if you had each in your hand you can tell straight away the quality, im pretty sure the $20 ones are just filters in a black box