I love Barlows, definitely my favorite pattern.
As has been said, the used market can get some gems and Boker makes a great Barlow.
Looking for old knives is a great pastime and anyone into knives should kind of always be doing it. Try antique stores, flea markets, gun shows. A local (great) knife shop pulled a box of used knives out from under the counter to my surprise when I thought to ask. Great way to feed your addiction for little money in lean times.
I recently got a Boker Barlow for $30 new at the above shop. I think they are normally about $40 but it was the last one he had. I'm real happy with it, good carbon steel and great fit and finish.
Utica makes a carbon steel Barlow for about $25 or so. I've read it has a weak snap and I actually read that some of the other Utica carbon steel knives have a stainless small blade. Still, people usually say they like it and that it is a good knife for the money.
I am the quintessential cheap b*stard for my work knives myself. I have a Rough Rider Barlow that sees a lot of back pocket time 'cause I payed about 7 bucks for it and I know I won't be scared to abuse it. Still, I find myself very unhappy with the edge on a regular basis wishing I had the 7 bucks to save for, well maybe an old, used, carbon steel Barlow.
Magnum Boker makes a Barlow for $10-$15. I don't think it is carbon steel and don't see it being better than a Rough Rider.
If I had the choice between the Boker and the Utica and the Boker was $10 more, I think I would go Boker. It's just a nice knife for the money. I'm talkin' Solingen basic Boker, not Boker Plus or Magnum Boker.