Don't waste your time and money. If you can't mimic or at least improve your accent by simply paying attention to how Rio Platense sounds, there is no chance any tutor will help. Native English speakers are the least likely ones to lose their accent in castellano, next only to asians. Your buddy Dustin fakes it somewhat successfully, but any porten'o will tell you after hearing half a sentence from him that it's forced. You'll be way better off Investing your time and energy in studying proper grammar, idiomatic expressions and jerga/lunfardo - they will understand your accent either way if you speak properly and they'll appreciate your knowledge of the dialect way more than a fake porten'o accent.