If you are looking for passive cooling in a fashion similar to the reserator, head over to ebay and search for "finned transmission coolers". You can get your hands on decent 18 inch single pass models for around $45 last time I checked.
Four of these will run you $180... with shipping... say $200. For the same price as a reserator you will get much better cooling (I cannot back this with empirical data as I'm too lazy to run a controled experiment). The difference is that you get more internal surface area, as there are fins inside the tubes, and more external surface area (rough estimate).
Your block selection will be a different story. Pure copper+pure aluminum transmission cooler+distilled water=a dead loop in no time. You could have the internals of whatever blocks you have gold plated, making them inert. I have no idea what this would cost you, though.
Another option is making your own radiator. Try this: head on over to home depot and pick up some 1/4" Cu tubing (buy 1 coil 50ft in length and split it into three equal lengths). Wrap it around a few 2" pipes (of whatever material you can find) to achieve this design:
The inlets and outlets for the coils can simply be epoxied into place in the reserviors. More seperate lengths of copper will yield lower flow resistance. Sorry for the crumby image but I put the design together in about a minute. If you need clarification just ask.