4" x 3" Rectangle
Priced per unit with quantity breaks. Vendors quote steps at 1 / 5 / 10 / 25 / 50 / 100 / 250 / 500 / 1000 units, and the per-unit rate drops at each break.
No. Postage is a carrier rate. Reputable vendors pass it through at cost and earn margin on printing and services, not on stamps.
Size, weight, and whether the design qualifies for presort and automation discounts. A small design change can move it into a cheaper postal category.
Related variants of this product are tracked as separate benchmark lines. Match the spec before comparing quotes.