It doesn't advertise much, and its gates are generally located out of sight, at the end of the Lambert-St. Louis International Airport terminal. The way most travelers find out about USA 3000 Airlines, it seems, is via good old-fashioned word o' mouth. In this case, they're words you wanna hear: "on time"; "no-hassle"; "funny flight attendants"; "cheap." The five-year-old carrier, owned by Apple Vacations, sells deeply discounted one-way tickets for direct flights from St. Louis to Canc?n, Mexico; Punta Cana, Dominican Republic; and Fort Myers and St. Petersburg, Florida. USA 3000 doesn't require Saturday-night stays, and fare changes clock in at only $50 (for domestic flights) and $100 (international). Instead of camping out in line for a good spot inside the airline's Airbus A320s, travelers can snatch up a seat assignment online for $5 if they so choose. What's more, last-minute deals abound on the USA 3000 Web site. With some more good chatter, perhaps demand will rise and USA 3000 could add St. Louis lift-offs to Los Cabos in Baja, Mexico; Chicago; and Bermuda.