I was heading down the lake in my new to me bass boat when the motor revved high and then the boat just wouldn't go, forward or reverse. Still runs and shoots water out but no moving. I can spin the prop in either direction with motor off and shifter in gear, am I in deep trouble or something inexpensive?

Spun hub??? Simple and relatively inexpensive fix at the shop, if so. If you have a spare prop, throw it on and you'll know real quick. If you don't, now you know why you should always carry one onboard

-T9

Yep, spun hub.  You should not be able to turn it if motor is off and in gear.

When you spin the prop by hand with it in gear, is the nut and shaft that holds the prop on spinning also?  If the nut and shaft are not turning when you spin it by hand, then you've spun the hub in the prop.   Nothing serious, any prop shop can replace the hub.

If the nut and shaft are turning when you spin the prop with it in gear, then you can say you've just had a very bad day at the lake, because something that's not cheap to repair is broke.  The only way to fin out is pull the lower unit to check it and to make sure the vertical shaft is still good.

Well it looks like a bad day at the lake, it's all spinning... was hoping for a shear pin or spun hub

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Lets check one thing before you get too sick.  Pull the cover off, and look at the two cables on the right front of the motor.  One is the shifter, one is the gas.   The lever the shift cable goes on goes under the carbs and connects to a rod that goes down to the lower unit to change gears.  Have someone move the shift lever on the boat back and forth while you look at the rod going down to the lower unit and make sure that rod is moving up and down also.   It seem strange the prop is spinning in gear and not making any noise.  Usually when something breaks, there is still metal contact and hear/feel it.

What year model motor is this?  If it does end up being the Lower Unit/drive shaft, it might be a lot cheaper for you to buy a good used LU from and swap them out yourself, it's really not very hard, than pay that hundreds of dollars labor and very high price for a LU or parts the dealer is going to charge.