Well My logic is that not many people will trade 3 um's for Ist or 2 Mal's for Um anymore.. although it does happen occasionally...
As for the Surs... They are extremely uncommon.
Because people have been Fg hungry lately.. Everyone is trying to sell their Runes as fast as they can... drastically lowering the prices of runes overall...as people are trying to sell cheaper then everyone else in order to sell faster. Im sure once the economy stabilizes, Ists will rise up in prices a bit...
Just my 2 cents