...inexpensive, high-quality lens? Just bake it!, article.
Simply put, a droplet of liquid silicone is applied to a curved substrate, then cured in an oven at around 158°F (70°C) for 15 minutes. After it's cured, further droplets are added and cured to adjust the curvature of the lens, and thus its focal length.
The result, says a white paper on the research, is a lens that costs as little as one cent, yet has comparable quality to a commercial microscope lens.