With Surtronics, they have 2 pricing categories. The first is basically small parts like fasteners that they can put in a big barrel bin that turns. They do as much as will fit in a 5 gallon bucket for around $75. This is clear zinc or zinc with dichromate. For cadmium, the price is higher. The other category is bigger parts, which they call "rack" items. Not sure how they price them, maybe by size or weight. If I take just about everything that needs to be re-plated for one car, probably looking at least $500 to have it done (including barrel), maybe closer to $1k by the time it's all said and done. Big pieces like the rear quarter slides and the bottom support of the door glass add to the cost.
Keep in mind that Ford used zinc plating as a "primer" on quite a few pieces. If one got crazy and did a bunch of parts in zinc, that would end up costing more too. I suppose when you compare the cost difference in epoxy primer vs. zinc plating, it might not be that much. Pieces that I can think of that were zinc plated before paint would be: shock tower to cowl braces, battery tray, bumper brackets, hood latch support and other big pieces typically painted/dipped.