Perhaps a layer of burlap for high strength , and a layer of old sheet or other smooth fabric on the top for smoothness...

Easy to do , still cheaper than canvas ...

Actually from an artistic standpoint, I actually Like the texture of painted burlap ...

You know , once the strength is provided by the burlap , even Kraft paper or newspaper would be a smoothing finish ... I’ll bet we could get a
Very smooth finish like that with a little extra priming and sanding ... another test ...
