Roberts,
No you're certainly not going to save any money with the koverall and dope method over iron on coverings. It took a gallon for me to completely fill the weave on my 90" /1,325 Sq.inch wingspan plane. This took 5 to 6 coats of Butyrate dope, and another 5 coats of spray primer, with sanding in between all coats. But I set out to accomplish a very smooth finish. I wouldn't think you are going to need anything near a gallon if your not looking to fill the weave. (of course much of what I applied just gets sanded off in the form of dust as I sand the surface down to a glass smooth touch)
I personally much prefer working with glass cloth, and will try to avoid future projects that have open bays not allowing glass cloth.