Don't have blueprints, but...
I'm in the middle of building a setup to handle 50L kegs.. The hardest thing to get is material for the heat exchanger (at a reasonable price

) I'd hunt arount in newsgroups (try melb.general, or aus.ads.wanted) for secondhand fittings, which will turn out cheaper than LHBS.
Also, it will be cheaper to find somewhere willing to bend you up a coil of SS tube, rather than getting a chiller plate.
So far, mine has cost me about $70 for all the components except the esky to mount it in, and the gas + regulator.
:chug: