Routers are actually uComputers (most on a level comparable to the old 486 processor)
Just like a computer that would freeze (or run very slow) if the mem is too low and the OS is too Sh**, so are the Routers.
Some Routers have open source firmware (the OS of a Router) so there is a chance to tweak their capacity with free 3rd party firmware (Like DD-WRT).
Price does not necessarily indicate a better Router; some Brands tend to be more expensive than the others regardless of quality.
Problem is that the Vendors that sell Entry Level Routers are getting away with Not providing technical data but instead floods the users with marketing verbiage.
If you read the data Sheet of most Entry level Routers there is No technical differentiation between the hardware, they look the same. They describe the Network standards that they supposedly adhere to without providing any info about the actual hardware of the specific device (Like, CPU, Chipset, Mem, OS, Clock speed, etc.)
Of the sub $100, some of the Models offered by Buffalo, Asus, and Zyxel, are somewhat superior in their hardware.
The rest are existing on Marketing, and the need of most consumers to stay ignorant.
That said there are many Entry Level Routers that consumers are happy with. That usually means that the user have one or two computers, used for ordinary surfing, email, and Wireless within no passing walls, or one wall.
However since most consumers do not tell you what exactly they do with their Router, it make appear like every thing is "Peachy".