Hi KWP,
I would recommend that you contact a local tire store and have them give you a bid. I believe your tires are:
ST235/75R15, Load Range C
but, they might be Load Range D
Look once more on your tire sidewalls. I usually get a bright flashlight and reading glasses to see the fine print. The information for your tires should also be on a placard on the outside of the trailer. For the location of the placard, please see this Thread and Tireman9's comments:
https://www.winnieowners.com/forums/...ml#post3947702
I would guess that, balanced & installed, the cost for four would be at least $800.
Eagle5