When I have a project, I usually have the store cut the 4x8 into slightly oversize pieces and then I neatly trim them when I get home. They do it for free or for a nominal fee.I doubt that you can do much for under $500, but I have not looked.
I suggest that you get one of those fences for portable power hand saws. You clamp the fence to the 4x8 and run the saw along side of the fence. They are not too expensive.