It cost less than the cost of an OC2 on ebay, that's for sure. I used an old 120 x 95 aluminium case, sockets and 3PDT switch that I had in my shed, so that saved me somewhere between £16 and £20. The actual components would have probably run to about £20, but again, I already had most of the stuff. The SK30 diodes, and the LM324, 4027 chips etc were probably about 50p each. I'm sure if I totalled it up it would run to maybe £40ish, but that would include 3 lots of p&p as I couldn't buy all of the parts from the one shop unfortunately.