Prototyping is an important part of the design process and has repeatedly been identified in prior work as an important tool for designers to test assumptions, communicate ideas, and develop design knowledge. Researchers, however, currently have a limited understanding of how the resources invested in a prototype influence designers' decision-making and their perceptions of a prototype's value. Prior work has shown that significant investment of time or money in a prototype can lead to undesirable effects such as design fixation, but the full impact of these factors on designers' perceived value of the prototypes remains unclear. Likewise, it is unclear how prototype usage impacts the evolution of designer knowledge. To explore these relationships, a study was performed in a 16 week-long design project involving 32 teams of mechanical engineering students. Results suggest that effective prototyping uncovered new design knowledge and limited uncertainty early in the design process, allowing teams to spend more time testing and iterating later in the design process. High-performing teams also reported final prototypes as less valuable for gathering new knowledge than their peers. Importantly, the study did not find any significant relationships between the cost of a prototype in terms of money and time, and the perceived value of that prototype. Nor were any significant relationships found between costs and final design outcomes. This work underscores the need for better methods to evaluate the value of prototyping efforts.