Kenneth,
I'm sure available dollars is an overarching limitation in many schools these days. Ways I have found to maximize the guest speaker is using vendors, product representatives, and recent graduates who are successfully working in the career area. Although inexperienced, they bring an enthusiasm that more seasoned workers may not demonstrate. Also, they are familiar with the school and the classes, so they can bridge the world of school and the working world in their presentations. Students sometimes relate to recent grads as "one of their own", and therefore get more out of the graduate-as guest-speaker experience.
Barry Westling