Can't believe no one has answered this one yet..Okay, if it is a Ruger, then it is .41 Mag..far as I know, that is the only .41 Ruger ever made...Pretty sure they have never made anything in .41 Colt..
for cheap holsters, check with Cablela's or Track of the Wolf..(TOW is basically a re-enactor supplier, but they do have some inexpenisve holsters listed...