You were probably looking at kits. Those range from about 40 and up (though I got a pretty good one for just under 30 at Walmart. It's definitely cheaper there)
Getting just a tank with nothing else is REALLY cheap no matter where you look.
Lights are totally necessary, especially for bettas, so you don't exactly need a hood or lid. Plus, with no hood or lid, you can semi aquatic or aquatic plants that can grow out of the tank "like Lucky bamboo" and it looks pretty cool.
With a small tank and a betta, you don't really NEED a filter, so you're good on that front.
In the long run, you'll want to get a heater, but you can wait until you get more money and they're not too expensive, really.
So going with an empty tank (instead of a kit) might be an awesome plan for you. :)