Well, I sort of agree. It'd be hard to buy in a movie -with a higher standard for suspension of disbelief- that a teenager living under such meager conditions would be able to develop a webbing with the strength and abilities that Spider-Man's does, let alone have the money and materials to manufacture it.
I get Peter is supposed to be "smart" but he's still a teenager living in a Queens slum and he's going to have all of the resources and avenues available to one -pretty much nothing.
There's a huge difference between being a smart teenage prodigy with a promising academic career ahead of him and being a teenager able to develop and produce loads of "webbing" that's stronger than steel, has miraculous adhesive powers when in contact with something (while only being "tacky" to the touch of its sides) and yet still degrades on its own over the course of a few hours.
Such a miraculous material would require very specialized chemicals, resources and machinery to produce. Something I'd argue would be well outside of the reach of a teenager living with his financially struggling aunt and uncle.