Why do you think flat doors are "too cheap"? Maybe old warped splintery hollow core doors.

You can do a variation on a flat door:

We have flat doors in our very much not cheap contemporary home. We love them and they work perfectly for the style of our home.

It depends upon how "contemporary home" is defined/designed.

Lots of options out there and definitely not cheap! Even if someone doesn't love a particular style they can appreciate the difference between a cheap builder grade door and a custom solid core wood door.

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There were a lot of houses built in the middle of the last century in the US with cheap, hollow core flat panel doors. When people refer to cheap flat panel doors that's what they're thinking of. As the previous posters have shown, there are more expensive, very attractive flat panel doors available. Maybe not at big box stores, but if you live in a major metro area you should be able to find them somewhere locally. The price of lumber has been all over the place the last two years, and while it's not at its peak, it's still high as compared to pre-pandemic, so be prepared for sticker shock.

Flat slab solid core, minimal trim. Kerfed corner bead drywall (trimless) is a great start for a few hundred per opening, higher end grooved doors add a few hundred more, concealed hinges add a few hundred more, pretty soon low 4 figures. Depends on budget. A few clients have used single inset flat panels, inset 5 panels, some with glass.

Here is mine. Love European style of interior door. Wanted to have something with glass but since I have very rough kids had to give up that idea. I was considering slab but I wanted a little twist to it. I chose those.

This local to us manufacturer offers flat doors in sequence, slip, random and bookmark matching in a variety of exotic hardwoods. Amazing what the colonists can do nowadays!