Being a boat owner I have to say that $500 for two people for a day of fishing is pretty reasonable, I figured out the cost of going out sturgeon fishing for a day on my boat with three friends to be $140 out of my pocket, that was just fuel, lost gear and bait, that does not include the cost of the boat($50,000),rods and reels(in my case $2000 for four set ups),up keep on the boat, fuel to and from boat launch, guiding licenses, advertising costs, liability insurance, boat insurance, launch fees and the myriad of other costs that I can't even think of that must go into guiding.
As an owner of a small business myself I know how these small incidental operating costs can snowball and I can tell you that if my small shop does not bring in between eight hundred and a thousand dollars a day I'm loosing money, and that is just me in my shop and does not include the cost of employees. I don't know how these guys even do it and still make a decent living, you have to remember also that they can't work all year and as business owners are not eligible for UI in the off season, so my hats off to the guides out there.
I usually go out once or twice a year on some kind of guided fishing trip and I can tell you that in one day on the river with a guide I learned more about fishing for sturgeon than I had by myself in three years of fishing(thanks' Vic) so even though it seems like a fair chunk of money to put out the wealth of info you will gain will far outway the cost.