Can you usually expect to pay around $500 to upgrade RAM? 1 Day is selling a refurbished iMac for$1249.99 which has 8GB Ram but they are selling the same model for $799 which has 4GB Ram at yesshop. I can't seem to find any difference other than the difference in memory.
http://www.1-day.co.nz/products/ACIDANZ63
http://www.yesshop.co.nz/handler/goods/GoodsDetail?goods_no=1002590&tracking=&sale_shop_sct_cd=00&disp_cat_no=100080000100008