Let me think on this...
As shown, a USB chip is required, the basic cost is 94p, a USB connector is 58p and the regulator £1.14 (not including delivery etc). In fact a connector is not really required - a USB cable could be chopped up and hard-wired to the USB chip.
Don't really need the regulator either if 3.3V supply taken from say a powered PS3.
IF we were to make the daughter-board PCB to support this idea and supply it with components fitted, plus time to make and ship (to the UK, more for abroad of course) then I'd hazard a guesstimate at about £15 all-in for the bits and bobs (<- includes delivery charges) and then £15 for the bare PCB (<- includes delivery charges). No 'profit' in that of course
'Customer' then gets the basic connection hardware onto which they place their ProgSkeet v1.2. Or just wait for a working BitStream for the v1.2 to appear.
Note: Connecting up to a single NAND chip is FAR easier than connecting up a NOR chip. If connecting to a NAND, don't need all that green wiring (directly to the FPGA chip) shown in the picture of my daughter board above.