[PokerAce]

Most custom work is custom because there's not much of a market for it. Something like this may be marketable, and you might get the developer to charge less in return for a cut of the profit if it goes commercial.

A lot of developers charge by the hour. I do custom work and charge by the hour. The amount they charge depends on several factors: experience, reputation and opportunity costs (how much they could be making doing something else). Expect to be charged between $50-200 per hour of work.

Also, development takes a lot more time than you might think. An application that accepts one hand history format and spits out another with no interface or configuration options may take 10 hours to design, write, test and deliver. So right there, you've got a good deal of money involved. Add in additional features and the time and cost adds up quickly.