Perception of quality in a paper is more dependent on the thickness (known as bulk), opacity and hand feel of the paper than its weight. This means that by carefully choosing your paper and suiting it to the communication goals for your print job, you can economize without appearing cheap. By selecting a higher bulk paper at a lower basis weight (a measurement to compare the weight of different papers at standard sheet sizes) you may save on mailing costs too, by reducing the weight of your mailing.
Significant savings are more likely on longer print runs. On shorter runs, paper accounts for a smaller proportion of overall project cost, so for these jobs you may as well indulge in top quality stock!