So which is it a2 or a3, you say both sizes.
Personally I use canon paper (A4 to A3) but I use canon printers. Generally own brand paper will give the best results. For A2 work I use Epson paper again on a canon printer.
Cost for canon a3 glossy is about £30 for 30 sheets iirc, although vat may be needed to be added on.