I have a $400 mattress with a $150 topper on it. It was a damaged Serta foam mattress (missing cover). It held up about 2 years before I bought the topper at CostCo.
Next time I buy a mattress it will either be a Tempur-Pedic, which we had for years and really liked, or a Sleep Number.
We bought a memory foam king set about a year ago - not Tempur-Pedic - and I think it cost in the neighborhood of $1K. That included delivery and hauling away the old mattress set.
Just had a new bed (Full size) delivered on Friday by Macy’s.
With the white glove delivery and removal of the old mattress, it came to @ $620.
Could have bought cheaper, could have paid more. Happy with what I bought.
We just bought one of these after seeing it compared to the “bed in a box” matreses that are all over the place now.
$239 for a king size, and it’s fantastic. I’d absolutely recommend it.
I bought a Tuft and Needle, too. Love it. I’m a side and stomach sleeper, so I didn’t think I’d be too fond of the firm mattress, but it has enough give that it’s very comfortable.
I reckon a decent bed is worth it, since you spend so much time using it.
My last mattress cost £500 (about $680.)
I like it. 
I sleep extremely hot. So much so that I can’t sleep on any foam. I always end up pouring sweat anywhere that my skin touches it. Even the latex foam and gel infused foam just a bit longer to get hot. The foam mattresses feel really great for my back, though. I tried several spring and hybrid spring/foam ones lately until I finally tried the Purple mattress. For me it’s the best by far. Similar to a foam feel, but it doesn’t get hot at all. It stays cool feeling all the time, which I love. I think it was about 1200 for a king.
I stopped sleeping on a mattress about seven years ago, the carpeted floor is just fine. My back feels great, I sleep soundly through the night. I was in my 70s when I discarded my mattress.
It took a few nights to learn to position my body to avoid uncomfortable pressure points.
Before that, I slept on the foam pad that I had kept in my van for camping, because when I moved, I didn’t take a bed along.
So I answered $0-500.
Sleep Number King, bought last year. We got the mid-range options, not all of the bells & whistles (memory foam layers, cooling, lighting). As for price, well lets just say it’s on the upper end price-wise, ('cause that’s how we do things 
)
I think my most recent mattress cost something like $1200, but we had to buy something to accommodate my spouse’s messed-up back. When it comes time to replace it I may well go for a less expensive option.
Just bought another latex hybrid mattress from Nest last month. I put the second option, though it might have been a bit more than $1k. It’s…okay. I liked the other model we had from them better, but it got ruined due to a plumbing leak, and we thought we’d try another model. Nope, the previous one was a little better. This one is not so good for activities, but isn’t all that comfy either. I’m a side sleeper and I often wake up with my bottom arm/hand asleep. Ugh.
Before that, we had a huge cushy no-name memory foam from Amazon for about $300. It was horrible for…activities…but a dream to sleep on. As long as you never wanted to roll over or get out of bed at all. We only got rid of it due to changing bed size.
Edit: Before all that, we’d had $2000+ traditional mattress sets that were in no way superior for comfort, at least, so I guess I’d rather fool around with cheaper mattresses in the meantime.
I paid $150 (reduced from $600) for a king size Ikea foam mattress. I think it’s comfortable, but my partner would prefer something firmer., though he’d sleep on the floor, if I didn’t object.
Paid something like 1200-1500 for a Select Comfort (now called Sleep Number) full size with split firmness about 12 years ago (maybe even longer). Still going strong with no issues, my wife and I both like it a lot.
Just got a full size Casper (o foam one they ship to you compressed) for 750 for my son (age 15). He loves it, of course his old mattress had seen better days.
I’m only 5’8", but I also have a California king mattress. It’s a knockoff of a Tempur Pedic, but it fits well with our bed and has been ok. I think we paid about $1200 for it around 8 years ago (at the time the name brand mattresses were well over $3k for a similar mattress and I honestly couldn’t tell the difference). I’m probably going to get a new one fairly soon…I’d like one of those kind that tilt up on each side, though not sure if they make them in Cal-king size.
I have a memory foam mattress that I like but it gets hot. I bought it after having heart surgery to avoid pressure points. If I were to buy a new one it would be the cheapest adjustable air mattress with a 3" memory foam topper. It would be the best of both worlds. If it sagged then I’d just add more air to it.