Viagra: 50-100mg, Onset ~60min, Duration 2-4hrs, Time to peak 30min-2hr.
Cialis: 10-20mg, Onset ~60min, Duration up to 36hr!!!!!, Time to peak 2hr.
The price difference between the 2 is less than a dollar. Cialis has better properties (longevity), but takes a little longer to work.
Hope this helps...