The best character generators for live events are often the most expensive. The leaders in the industry are Chyron and VizRT. You may visit the Chyron forum here on the COW.
On the less expensive (but with less features) list, I would include Compix.
How is the rest of your van outfitted? I freelance with a guy who has 5 ancient but workable 1/2" cameras with studio kits, a 16-channel audio board and a used single-channel Compix. He produced a 10-week package of local high school football games for the CBS affiliate here. Not network quality, but with a budget that made it worthwhile for the station, the producer, and the local crew.