Like most consumer items tents have a point of diminishing returns. A $300 tent is not twice as good as a $150 tent but if you want that extra refinement you have to pay.

Personally, I have been using a $50 Coleman 7'x7' dome for over ten years. My whole family slept in it when the kids were young. It works for me because I don't push its design limits. I have other more expensive tents too. But when the weather is nice and I don't care about weight I still reach for the Coleman.

I think your original question is rather incomplete and overly simplified because you did not specify any requirements. Does your tent have to be light? Do you need bug protection? Do you camp if rain is in the forecast?

Sure you can buy that $20 dome and it may work fine for you.....until you ask it to do something it wasn't designed for. Like being durable or withstanding high winds.

Price and true cost are not the same thing.