Both Larry M and myself have build from Sanjay's plans. I was a lot of fun and easy to build with no real special tools required.
Reactor itself only cost about $40-60 to make. Expect the total to be around $200 after all the CO2 equipment and recircualtion pump is added.
http://www.aquariumfrontiers.com/fis.../2/default.asp
And here are Larry's notes/modifications:
http://www.reefcentral.com/northernr...um_reactor.htm
I have a 90g heavily populated tank with SPS. This unit easily maintains my tank at 10-11 DKH and 420-440 CA.