One thing I would try is to jack up one wheel and put the car safely on a stand. Disconnect the shifter cables from the transmission selector. Manually move the selector into neutral and then into the various gears. Check to see if the wheel spins freely in any location. Also check the lubricant level in the transmission.
I suspect, as you probably do too, that something has gone wrong inside the transmission. That price of $300 for a replacement is a good deal but the price will probably go up as the clutch kit and other parts are added to the installation.
BTW how many miles on this Accord?
Good luck on this