bigdrums2;418802 Because you are talking about using plastic mulch I am assuming your vineyard isn't too large said:
An acre of vines is 43560 square feet divided by 8 feet equals 5445 feet of row, so one single 6000 foot roll will do an acre allowing for a bit of waste at ends. A 6000 foot roll is between $150-200 so I hardly think the cost is enormous. Since the plastic is basically inert and will be removed before the vines bear, they aren't much of a cause of contamination of the soil.
The original poster asked about plastic for weed control. The idea of compost (while great for the soil) does nothing to address the weed problem and by your admission adds to the weed seeds.
As far as the last statement, almost anything can contaminate the soil, even compost. A member here on the forum (through no fault of his)has a small farm he bought which had a couple areas contaminated by composted manure which was from hay fed to horses from alongside the road which had been sprayed with an herbicide. Almost anything CAN hurt the sloil so we all need to be diligent about our own growing areas and keeping them clean and safe.