A plow truck sees a LOT of loaded, low RPM time. Just the type of operation that needs hardened seats.
I love posts like this where people always want to do a job on the cheap but what they need is the exact opposite. What difference does it make what the truck's worth is as a static hunk of metal?
What's it worth as a good operating plow truck?
All this talk about "it's not worth X, so I am not putting Y into it makes no sense to me.
Either fix it right, or throw it in the ditch.