You are either going to spend $985 or more for new, or search the boneyards for a used ROPS that will probably run $500 or more. I have never priced out an aftermarket ROPS for a tractor that size under $1000.
Some states have reimbursement programs that offer some cost sharing, but as you joined anonymously, I can't help in that regard.
Sometimes to get the best info you have to give some up.