As the Bakabaka commented this is definitely something you should consult with your printer.
The exact practices and prices may differ between countries, however, in general, the prices depend on the printer sheet areas and number of passes through the machines (in the case of offset printing or some additional enhancing processes). In other words, in most cases, you'll pay for the number of sheets printed, not the number of arts imposed on the single sheet. Of course, it's possible that some printers will modify the prices based on the quantity of paint/toner used or some other factors, but that's when the “ask your printer” comes in :}.
If your printer uses sheets in printing process, you should ask about the biggest printable area available to you (net printable area). Then, you'll be able to “simulate” how many of your artworks are able to fit on this area. You must also take into account the potential bleeds and trim marks, but it's a good estimator of how efficient your format is—the more arts you can fit on the sheet, the cheaper your print will be. In extreme cases you may try to do the imposition yourself and send your printer the complete image of the sheet. There are times, when it's worth to do that. All the single arts will be cut out of the sheet after the printing is done for (most of the time) negligible price. The “standard” size does not help much, at least in the case of reducing the price of print.
The bottom line is, you should be more concerned about the maximum printable area than about standard paper size.