Classic Thonet Bentwood  

you can get them from twenty ...
you can get them from twenty twentyone here in the uk
http://www.twentytwentyone.com/displayProduct.asp?ProductID=981&x=9550

or these are in a similar...
or these are in a similar style in the US, not sure if they would work with a dining table though
http://www.conranusa.com/ProductDetails.aspx?pid=20338&cid=ChairsStools&...

Both close
Yowza at the price from 20/21. The Ernst chair is so very close - but you're correct, the arms wont work. At least there's hope that they're still being made!

Still in production, not hard to find
You might take a look at Bauhaus to Your House (link below). A tad pricey, but not completely insane. Or make it a thrift quest: I passed up four of them, with nice patina (needed only minor tightening up), for six bucks apiece last week.
http://www.bauhaus2yourhouse.com/_Thonet-dzr42?gclid=CJuu1_aA_ZQCFQSwFQo...

ugghh
These were supposed to be the cheap alternative! lol. I may have to rethink the vintage option. They ARE beautiful tho!

What would you value a...
What would you value a vintage Thonet bentwood desk, circa 1950, with a laminated top. It's a small desk with one drawer.
Just saw it recently at a resale shop and was thinking about it. I think it was $100 or $120.

At
31" high, and with the arms dropped a bit, I would think the Ernst chair would fit nicely under a 30" table with a thin top. . .

. . .or not
I don't know.

LuciferSum, you're building...
LuciferSum, you're building a case house, aren't you?
It seems the Thonet company is alive and well. The classic number 14 is now designated 214 ( http://www.thonet.de/)
Is that number 18 in your photo? They are both beautiful. Model 18 looks to be more comfortable, and it says it was the largest selling model. I would get the 14 myself though.
I can't see the manufacturer of the chairs in the previously posted links. The bauhaus2yourhouse page only says they are "made in Poland" as licensed reproductions, and that they are "...manufactured by original European Thonet factories in Radomsko Poland, and Brno, Czech Republic, using historic molds and techniques.."
The prices at Einrichten Design, a German online store (see linik), are higher, but there is no mention of the manufacturer.
What table will you pair them with?
http://www.einrichten-design.de/Thonet::H22.html?language=en

Sturdy, you say? How's this for sturdy and cheap! Bentwoods are always showing up on CL around here anyway. http://sfbay.craigslist.org/nby/fur/782988157.html

Hard to find? There's a set...
Hard to find? There's a set in my shed you can have! Thonet produced millions and then there are the versions by Kohn, Mundus, Fischel etc etc. Just search Ebay for 'bentwood' or 'cafe chair' and you'll soon find a set

If you decide to get used one...
If you decide to get used ones, don't pay a lot. They are held together with screws. As I'm sure you know, the screws are much harder than the wood and wear on it with use, making the screw holes bigger and the chairs wobblier. We had a set that I eventually gave away because they just got to a point where they needed work all the time. We did use them a lot, though. If yours will be more for looking at than sitting on, go for it.
I paid $8 per chair years ago and I don't think they've gone up much since then at estate auctions around here.
They're also rather small and not all that comfortable if you like to sit around the table and schmooze after dinner.

Ikea
Ikea did some repros - in plastic!! Not quite the same! But then I have an Arne Jacobsen series 7 in plastic.

Opposite
I'm actually trying to create the opposite of a case study house. My boyfriend's tastes run more toward colonial/federalist. I'm trying to find something that would bridge the gap between modern and traditional. I've always found these chairs charming, and I think in a deep red paint they would be brilliant against a more traditional table.
In searching the web I've seen some more generic bentwood chairs that might work as well. Not as elegantly proportioned as the 14 or the 18, but cheap and maybe a substitute until the real thing can be gained. I'm pretty handy and I think I can keep them in decent shape. As for comfort - I'm more informal than most - frequent dinners on the coffee table, and breakfast standing at the counter. They will get some use- but my collection of lounge chairs will be the place to chillax after dinner.