Switchgrass pathogens problems

Ok, so right now the switchgrass pathogens project is in dire straits. So far, I've been unsuccessful in growing uncontaminated cultures. I'm getting lots of bacteria in my cultures which ruins them. I looked for Rifampicin in all my supplier catalogs and didn't find any. (That's the antibiotic we put in the media at UT last summer to prevent bacterial growth.) I emailed UT to see if I can buy some from them and they aren't really set up to do that, but she told me I can buy some from Fisher Scientific. They have 250mg for $34 but it is in powder form. It is only soluble in things I cannot have in a high school lab, like chloroform. It is slightly soluble in acetone and methanol, so I may have to try that, but Fisher can't tell me how I make it into a liquid, so I'm back to the drawing board. My contact at UT did tell me I can put one drop of lactic acid into each petri dish as I pour my agar, and swirl it around to reduce the pH to a level where the bacteria will be inhibited, so I may have to try that. I'm getting a little flustered though. I just knew I could make this work for my students, and now I'm not so sure.