factor30 is quite right; by far the biggest cost in these shares is the difference between bid and offer prices. I own some shares in a penny stock (as noted, this is gambling money only). On a recent day the bid was 50 cents, the offer $2. Meaning that if you wanted to buy you'd pay $2, if you wanted to sell you'd get 50 cents. Most trades actually occur inside these quotes but the swings can be dramatic; last week the stock went from $2.10 to $1.45 to $1.25 in the space of three trades (obviously someone was selling).
However, the true "value" of the company will only be realized in the long run (I'm hoping they get acquired for $10/share some day in the distant future) so darting in and out of the stocks on a daily or weekly basis, once you add in brokerage costs and tax consequences, is not likely to be a money-maker.