Is this one a tube that is just wrapped a certain way? 'Cause I like it lots.
In the photo, looks like an infinity scarf, not a tube, just made with bulky yarn and wrapped around multiple times. If you use a bulky yarn, or multiple strands, and an extra large hook, you get that effect. I could be wrong about the tube, but you'd have to read the description of how she made it to be certain.
If she did make a tube, that would use a ton of yarn, hence the big price, but I sort of doubt she did. But, it's so long, that it may have cost her a bit in materials. Bulky or super bulky yarn is getting quite expensive and there isn't much on a skein, the more bulky the yarn, the less yardage on a skein.
ETA: I read her site and she says:
Quote: So, not a tube. Of course, if there is something you like that we don't have, be it style or color, you could ask about it, like that expensive infinity scarf in the oatmeal color bulky yarn. i'm sure Ladyhawk or I could do one for you for less than that by custom order. Just would have to purchase the yarn and do it.

They really aren't difficult, but just take the time and materials to do. A skein of super bulky yarn can have as little as 64 up to 108 or so yards on it, whereas regular worsted weight yarn may have 200-370 yards for about the same price, but price depends on the quality of yarn as well. A scarf like that could take 3-4 skeins of yarn or even more, depending on the length/circumference you want or need and how much yarn is on a skein of the chosen yarn. We measure ours from the back of the neck to the bottom of the cowl, to tell where it will fall on the body of the person wearing it.
Also adding that the cost of one skein of bulky yarn varies a lot. We use mostly good quality acrylics which are easy care and more affordable, but they can range from $3 per skein up to $10 per skein. Ive seen some heavenly bamboo yarn that feels like silk for $8 per skein at Hobby Lobby, but can't recall how much yardage is on it.