Welcome to the forum Albert.

There are six different models of "barrel" Carrera:

110.515 CHN

110.571 NC

110.573 B

110.573 F

150.573 B

150.573 F

For a long time, these were the forgotten Carreras and were available considerably more cheaply than most of the other generations. However, the last year or two has seen a renewal of interest in these models, possibly as the 70s come back into fashion - these barrels are really an embodiment of that decade (in a good way). They wear quite differently to any of the other Carreras, sitting quite high - I'm a big fan of straps but for these I really advise looking out for the bracelets too. The bracelets may be less elegant than the Gay Freres of earlier generations but sit very harmoniously with the watch.

As far as values go, these were typically hitting maybe 2/3 to 3/4 of the price of an equivalent 1153, if not even less. With the growth of interest though, the prices have strengthened somewhat and you'll be paying closer to that 1153, though the barrels should still be a little cheaper, maybe 75-90%, say. Increased interest though also means diminished supply, so the search for one will take a little longer than it would have done only a year ago, especially mint or NOS. Caliber 15 models were originally a slightly cheaper variant than the 12s but the prices are roughly equivalent now. Blue and fumé dialled versions are the easiest to find, the gold-plate/champagne dial (magnificently 70s as it is, the example above is mine) is a fair bit rarer and the PVD model is rarer again. Rarity doesn't always equate to value though, the gold-plated one is not typically more expensive than the steel ones. A fantastic condition example with fumé dial went for the most I have ever seen a barrel go for at the recent Bonham's auction of the Arno Haslinger collection but you'll be hard pushed to find another as nice as that one was.

To summarise, I think these are on the up and are worth getting into now. Quite a statement watch too. Good luck with the search!