Next is the heat sink. Tomorrow I will visit a salvage metals store that is aimed at DIY folks like me. They have a big stock of aluminum extrusions at very low prices. I hope to find 2 or 3 inch channel extrusions, so I can put 8 LEDs on each of three of the channels, then join them, side by side, with aluminum washers separating them for air flow all around each channel. These will give me at least 24 square inches of surface per LED, with enough thickness to also store and easily conduct the heat to the air. At worst, I can buy the channels on ebay, again, for about $30, much less than the cost of a finned heatsink extrusion.
I have spent about $28 so far, not counting the heatsink or LEDs.