A lot of elements were rushed. Some strange plot points, like how he invents the webshooters (hint: he does the equivalent of ordering them from ebay). They rushed other plot points (Uncle Ben's death) or they aborted them halfway through (Spider-Man is hunting down Uncle Ben's killer, gives up after a while).
He orders the webs, not the shooters. The webs are widely available, he just creates a mechanism that allows him to harness them in the way he wants. It makes a lot more sense than him coming up with a magical wonder-chemical that would probably take years and years of research to make, and it's better than organic shooters because it's another instance of solidifying Peter as A Smart Kid.