You can cut costs a lot just buying Randolph brand dopes from Aircraft Spruce or other Homebuilt suppliers. Good stuff, quarts or gallons. Maybe you can pick it up and save on shipping at your local airport supply store? I'm partial to butyrate dope, because it's light and easy to repair on open framework wings, etc. If you build solid fuselages and sheeted foam wings, there are a lot more options, such as glass cloth with epoxy resin and epoxy paint, for example. It's way more durable, but I don't think anybody prefers the shine of epoxy over the shine of buffed clear dope topcoats.
Steve