i see that shops sell at a fixed price of 17 gp ea (i'm talking elemental). are all shops throughtout the game the same price? what other sources can people buy runes at lower prices?

yeah, following the shop update, all shops sell for the same price, with the exception of the zammy mage in level 5 wilderness. Your other options are buying in banks, buying on forums or using the grand exchange. i prefer the forums myself as you can scan threads to find the cheapest seller.