Hi, all--
I think we can all agree that the golden ideal is that all OP events are run for free, and lots of people turn out for them, and then they all spend a lot of money in the shop and make the effort worthwhile for the retailer. Everyone has fun, the retailer makes a living, and we all expand our gaming horizons.
Unfortunately, that's not always the way things work. There are a lot of costs associated with maintaining OP space--not just rent, but especially the staff cost for the extended hours (most OP takes place into the evenings, when the shop would probably otherwise be closed).
As the guy responsible for wrangling D&D Encounters and WWDDGD events in the UK, I would love it if every retailer ran these as free events--but I respect the fact that every shop faces its own unique situation, has its own OP policy and strategies, and manages a unique relationship with its local player community. The decision on whether to charge is up to the retailer.
In the case of the original post, $5 seems pretty steep to me--high enough to be prohibitive (as it proved in the case of the poster). In this situation, my advice would be to point that out to the retailer.
But I would also urge anyone who is provided, by their FLGS, with a nice space and great opportunities to try new games and meet new gamers, to recognise that that has value and is a cost to the retailer, and not be too stingy with the odd OP fee.