I need enough ply to cover my 16m^2 kitchen floor. This works out as 6 or 7 sheets. Wickes seems expensive at £23/12mm sheet or £27/18mm sheet. Is this expensive for WBP ply or is it about what I should expect to pay? Ideally I'd be able to find a supplier with 15mm in stock but it seems to be less common. Around the Brighton area there is Travis Perkins, Jewson etc, but they're not open today. Are these places usually cheaper? Is it worth trying to blag a trade card from somewhere?