A couple of folks have had trouble finding a few components, since domestic sources are stocking less through-hole stuff now, and more smd. I can offer a "mini-kit" which includes the troublesome items, as follows:
Mini-Kit (unassembled)
1 x 2 port PCB; R1.23a
1 x U2; CD74HCT123M SOIC16 package
1 x U1; LM78L05 TO-92 Vreg
2 x R3/R4; 3362P 2K 1/2W trim pots
1 x L1; 22uH 290ma, 22uH axial lead inductor
Package Price: $5.75 Add $1.00 to have the U2 chip pre-soldered in and tested.
All you need on top of this is about $2 or $3 dollars worth of inexpensive readily available caps, resistors and diodes to finish the project per the BOM. Please limit your order to a max of 4 mini-kit boards, as I don't have a limitless supply of the components on hand. 
The original base board/chip pricing is still in effect per the OP, as follows:
Bare board only: $1.60 each
Board with SOIC chip loose $2.50 each
Board with chip installed $3.50 each
Rod
