This is a 3-pin charlieplexing board, so that makes n^2 - n = 6 LEDs.
This board makes use of the smallest size on OSHPark, which is 0.25x0.25 inches.
That's ¢30, delivered. (Please order more than that, though! OSHPark deserves your support ;) )
It uses 0603 LEDs and Resistors (for red LEDs, I'm using 75 Ohm. Remember to halve the resistance because of charlieplexing --> two resistors in series with LED in between!)
A reel of 100 0603 LEDs can be found on Ebay for $4. The resistors cost me $1 for 100.
Oh, both of those have free shipping.
So, these things have a per-unit cost (without headers) of ¢10 + ¢24 + ¢3 = ¢37.
That's pretty good, right?