How do you feel about using water? If you're really worried about it and want to use as little as possible, then a more efficient chiller might be the way to go.
If you're less worried, or can re-use the warm water generated (I've been using mine to wash up brewery gear and fill up the washing machine), or you can use tank water and return the water to the tank, then run the chiller at full flow. My guess is that for the sorts of temps and volumes we're talking about, a standard chiller will only take a few more minutes to get you there than a fancy one.
FWIW, I made my own rib-cage immersion chiller from a roll of annealed copper from bunnings (6m roll, which was on special at around $100). Took about 3 minutes to build by rolling around a corny. Works well but I could probably have gotten away with using half the length and making a standard chiller, especially now that I've set up whirlpooling on my kettle.
Like I said before, my guess is that whirlpooling/stirring with a bog standard chiller will beat a fancy chiller with no stirring, so I'd lean towards not spending the extra. If you don't whirlpool, just using a sanitised spoon/stirrer every few minutes will really increase the chilling rate.