I completely agree that they don't necessarily have to be expensive and there are a number of expensive shoes out there that aren't worth the money. I just haven't found good shoes that are cheap. Trust me I've tried. There are occasionally sales as a company tries to clear out an old model of shoe.
You can get a good deal, but I haven't seen a pair worth having that ran less than around a $100. Ray Rose are in that range and so are SupaDance. My shoe of choice is the DanceNatural and for a lot of good reasons. A lot of their shoes are in the $100-$150. I like the gold heel so I'm paying a premium and they hold up like nothing else in this world. Their dance boots are in that range and in my opinion entirely worth every penny.
I am a devotee of a good dance shoe. I've felt the difference and I'm willing to pay for the advantage in balance and foot articulation. I would never pay that kind of money for a street shoe and in most other things I'm a skinflint.
If you are a beginning dancer, you have a year or two before you need to buy a good shoe but eventually it is necessary.