Decide how large a windshield you want. How much coverage do you need in the climate you ride in?...Hands covered?...coverage down to your turnsignals?...how much width? You want the top of the windshield to be just below your light of sight, and anyone handy with tools or a plastic or glass shop can trim one.
Memphis Shades and National Cycle are two good brands; there are others. Some sort of quick removal mount is good for those nice days when no windshield is needed. As always, beware of mailorder outfits with low prices that really chisel on the shipping charges.
Motorcycle Pro Shop and BikeBandit.com are two good ones; BikeBandit has a very liberal return policy.
I bought a National Cycle PlexiFairing GT and trimmed the top down for the height I needed. It offers excellent coverage which I wanted in my cool climate. This one isn't listed for the Savage/S40 but fits fine--and I had the BikeBandit return policy in case it didn't fit.