If you really can only get ATT and Comcast, then you obviously can only get what they offer
There are very few real Internet providers where I live (Toronto, Canada), but because of certain regulations the big providers allow third party resellers to buy their services in bulk and provide them in whatever retail packages they choose. So with a few of such resellers, we can get Internet-only plans that are much more competitive than what the underlying wholesale provider offers to retail customers directly.
Example:
- Bell (large ISP) offers 50/10Mbps (download/upload) service with a 175GB cap for $87 (they offer a $4 discount for bundling it with TV/phone service, for a reduced price of only $83)
- Teksavvy (smaller ISP which resells Bell's services) offers the same speed with a 300GB cap for $55, no bundles required.
But that's on the higher end. Their cheapest service can be had for $44 with Bell for 5/1Mbps and 20GB cap, or $25 with Teksavvy for 7/1Mbps and 75GB cap.
As you can see, it's all about having some competition. Going off tangent a bit, but here in Canada various organizations and companies like Teksavvy fought very hard to make sure Bell and the like are obliged to offer their services at wholesale to enable this competition. Big ISPs received significant government assistance for building out their infrastructure back in the day, and that's how they are made to pay back.
The thing that I hate about Bell is their varying prices. I just signed up for Bell Fibe internet, which is fiber directly into my house. The speed is 50/50, with the 175GB cap. It's crazy fast. It's $86 or so, but I get a recurring $34 discount, plus the $4 bundle discount, so it works out a lot cheaper. That's great for me, but crappy for everyone else. It should be just one price for everyone.