I use the AISC manual for steel construction, thats American Institute of Steel Construction... i dont know what the international standard is. the steel i posted is HSS, hollow structural section. the size i posted id the smallest available, once you go below that size you are using steel tube, that falls outside of my realm of experience because its not structural.
theres two ways to go as far as $$$, use steel with a smaller section and use more of it, or use a larger section and less material. you have to find out whats available to you and at what cost and make that decision. keep in mind that the thinner the material is the more difficult it is to weld
you hve two good looking stands posted already, your sump should still work with the one i posted, if you notice there is no bracing on the ends.
and the stand is pretty open in samsons design as well