Relationship between Effort and Costs
Fixing an error in the early product development phase costs about 2-10 $
Fixing an error in the late product development phase costs about 500-1000 $
Conclusion: the more effort at the beginning, the less cost at the end!
(ref.: Barry Boehm, Software Engineering Economics. 1981, Englewood Cliffs, ISBN 3-7719-6301-X)