Cheap is a ways away. My early projections would price each module around $75, so for an equivalent to the Procyon would be about $400 after you get a power supply and everything.

I have a hard time believing that heat will be a really big issue. I have a 650 watt power supply in my computer that is 85% efficient and it puts off very little heat. According to the datasheet on the K2s, they can be mounted on FR4 (regular PCB material, without metal core). The trick is using their pad design, coupled with a heat sink on the reverse side.

I am going to try digging around for some temperature info from other posters, perhaps someone could post their normalized heat sink temperature or the temperature of the metal core on their Luxeon Star.