That's the problem, the older lenses were for film, so 28mm was wide and popular as was the 35mm. They are what you can find cheap. A 24mm or 20mm is probably at least twice your budget. The 18mm on a kit lens on the D5100 is about like the field of view of the 28mm, so most the time it is better to just use a kit lens for something cheap on the wide end.