Thanks guys. I have posted in the FB developer forum. I still don't know how much I should charge? It seems (to me) like a fairly simple app. I'm very reticent to share details, but the only thing I can think of that would be complicated would be the Facebook Credit API. I don't know if this app would be "allowed" to use Facebook Credits, but if it is, that's the only complex part I can think of. The rest is incredibly simple from an algorithmic standpoint.