I wouldn't suggest using 1/4 of the velcro as it seems a bit to unstable to me and may not be easy for smaller kids to stick together. I also tried, on some blocks, to put velcro on multiple sides but when I tried to play with them it didn't work out as well as I'd hoped but your mileage may vary.
For $2.50 I would have been able to make 16 single-sided blocks. That makes each block worth $0.16. With some blocks having 1/4 of a velcro dot and some having multiple sides I was able to make 25 blocks ($0.10 each).
The creation part is simple, cut the velcro dots in half and attached 2 to a block. I tried to make sure each block had 1 hook and 1 loop each. These blocks are too small for a full dot but I didn't see any slightly bigger ones at the Dollor Store at the time.
I think these would be good for a road or airplane trip. They pack small and light and aren't vary likely to roll away. If you do happen to lose a couple it's no big deal price wise or "complete set" wise.
DO you think you know anyone that would like some building blocks?