A few years ago we shopped for a mattress here in Silicon Valley. Size was California King which is, IIRC, 4" longer than a standard King, but 4" narrower. First mom-and-pop store we went to, prices were $599-$3000ish. Running a "no sales tax" promotion (they always are).
My wife and I spent an hour trying different beds and through all the firm and soft and plush and ultrafirm ultradeluxe ultraplush nonsense.
Talked to the salesman, and he pretty much said the only difference between the REALLY low end $599 ones, and the $799+ ones, was coil count. Once you hit 799+, he told us, it was all kinds of toppers and so on. But the coil count doesn't effect warranty or how often you should replace it.
My wife's favorite bed was the $599 simple firm one. That was my second favorite by a narrow margin; my favorite was way down her list.
Delivered to our house a day or two later; again, no sales tax, no need for a box spring because we had a platform bed.
It's still a REALLY REALLY industry, and I'm not saying Americans don't pay more than they should, but I'm not sure our price range is particularly out of whack with what you saw, and this is for coils, not foam.
At Ikea you can easily get a cheap foam mattress; we have one in our guest room. I've slept on it when I'm sick. It's fine. I don't prefer it, but if it's all I ever knew, or if I spent as much time on one as I've spent on coil mattresses, it might well be my favorite.
Yet, not many people here buy foam mattresses, or mattress from Ikea at all.
Perhaps the bias is just that Ikea = cheap, but some trendy internet-advertised foam brand with a new name and a fresh face must be some new high-tech amazing thing.