You don't need a Zone VI modified meter to work with expansion and contraction, nor even a spot meter, but a spot meter can make life easier for checking brightness ranges.
You might consider a Luna-Pro SBC which is very good for measuring brightness range, and can accept accessories for limiting it's field of view. They sell for <100 USD.
I agree with Wade that a Crown or Speed is a good economical way to get into 4x5. A speed is especially good for economy because you can use shutterless lenses which are much cheaper than shuttered ones.