This work focuses on characterization of the mechanical performance of additively manufactured fiberglass and carbon fiber–reinforced composites fabricated with varying amounts of fiber content using a Markforged X7 printer. Samples were subjected to tension and three-point bending tests, evaluating the nominal increase in those properties per unit cost in dollars and mass. Samples were also scanned using X-ray computed micro tomography (µCT) to characterize their internal structure. Test results showed that the tensile strength and stiffness of carbon fiber–reinforced samples improved with each increase in fiber volume fraction ( V f ), while fiberglass-reinforced samples showed diminishing returns above a V f of 22.3%. The bending strength and stiffness of carbon rose monotonically with every increase in V f and plateaued for fiberglass above a V f of 17.8%. Carbon outperformed fiberglass in both tension and bending stiffness per gram. Carbon had a much higher tensile stiffness per dollar than fiberglass, while the bending stiffness per dollar of both fiber types plateaued above a V f of 5.2% for fiberglass and 6.5% for carbon. µCT analysis showed considerable void content with a lower average void fraction ( V v ) for fiberglass than for carbon. The V v of fiberglass decreased with increasing V f , while the opposite was true for carbon.