Get an old scrub plane to rapidly bring it down in thickness. If my old plane is a guide, they don't need to be expensive, nor do they require a a lot of fancy fettling. It's a rough tool that hogs out a lot of waste. Finish up with a hand plane.
Or find access to a bandsaw with the required capacity.
A thickness planer would also work. See if there is a tool rental company in your area with something that would work. It would be cheaper than buying a tool. Most allow 4 hour rentals for less than $100 depending on what is being rented. I have also seen ads on Creig's List for people renting out their tools. An other option would be to see if a local custom woodworkingr/woodmill shop would run it through their planer or band saw for you for a reasonable fee.
Brenda
1998 510 upgraded to a 520, upgraded to power pro with double tilt and lift assist.
1998 bandsaw
2016 beltsander
jointer
overarm pin router
Either on your radial arm saw or shopsmith ER, set up to rip fence slightly more than 1/2 from the blade. Set your blade height as deep as you can and rip along one edge of the board. Flip the board end for end and repeat on the other edge. You will now have two deep grooves separated by somewhere between 4.5 to 5.5 inches of material. Use a handsaw to cut through and you will have a board 10 inches wide and roughly 1/2 thick.
Gale's Law: The bigger the woodworking project, the less the mistakes show in any photo taken far enough away to show the entire project!
there is a woodworking club in Madison that might help you
see if they can help you resaw your board or plane it for you
besides that you can make some new friends
Madison Woodworkers Guild
6014 Gateway Green
Madison, WI 53716
Contact: Steve First
Phone: 608-222-7581