Aexalon
Explorer
Perhaps of more use, "A Magical Medieval Society: Western Europe" lists iron at 1sp/lb, and worked iron (bar or sheet) at 1gp/lb. Since your cube is 0.26-0.28lb (cast or wrought, respectively), I'd say 2-5sp, depending on how perfect the cube needs to be. As for steel, a multiplier of x5 to x10 is probably in order (before Bessemer in the 1850s, steel items were essentially VERY labour-intensive to produce), again depending on the advancement of metallurgy in the location of purchase. So, 1-5gp each, imho.