285907 Joomla Virtuemart Shipping

Im looking for a coder that will give me the following options in virtuemart... When adding products to Virtuemart i would like to have a field to add the postage for that product only. If a customer buys 3 of the same items at £2.50 postage i dont want them paying £7.50 postage. If its the same it should go by the standard £2.50 + a small % of the other products postage cost If a customer buys 3 products of all different sizes the shipping calculation should then take it from the biggest shipping fee plus a percentage of the other products postage i would really appreciate all enquireies towards this project.