I haven't recently seen anyone advertising wc Candoia, and I'm not sure they are still being imported. I remember reading that some of the Pacific islands where they occur had stopped exportation but don't know if ALL Pacific islands have stopped. From my own experience, most wc are going to be older animals - at least a year or two old at capture, if not more. Some settle down with gentle handling, but others like my girl are a bit more....fiesty.
It's taken almost two years, but she & I have reached a point where I can usually remove her from her tub (while wearing leather gloves) and place her into another without a strike. Any handling longer than what it takes to move her tends to cause multiple strikes and bare hands seem particularly appealing. Maybe in the next few years I'll be able to handle her, but at this point I'm not betting the bank on it. lol My wc male has always been quite gentle and calm. He just wouldn't eat - had to start force feeding him after several months when he started to lose weight. Believe me when I say I tried just about everything until chance happened to land some baby field mice in my lap for me to try...and that's what he liked. Now my mom breeds field mice for me. 
Wild caught can definitely be a challenge, but with these little beauties the captive bred neonates are still often a challenge in their own right. It's pretty much a given that, if you're going to breed these, you have to have some appropriately sized anoles, geckos or frogs on hand when the babies are due. Some neonates will simply take pinkies (those are the really coveted ones! LOL) but many still take alternate prey for the first few meals. It seems the captive bred animals switch to pinkies easier - either plain old pinkies or ones that have been scented. Also, if their setup isn't right (read as dang near perfect) they will go off feed as well. There's just all kinds of excitement in owning these guys. lol Don't let that discourage you from considering these guys as pets (or even a breeding project) though. They are some of my favourite pets out of my collection (28 snakes total, covering a number of different species). They are some of the coolest looking snakes out there IMO and pretty easy to take care of once their needs are met. Feeding problems are the main complaint I hear of (or experience), so the rest is just making sure your husbandry is right.
As for the prices, I'd be surprised if it were actually Isabels that were running $18 each - I've seen normal phase (pale tans & greys to darker browns & greys) go for as little as $20-$25 each at shows here (central Virginia) but haven't seen Isabels for less than $100 (and I jumped & purchased her as soon as I saw the price!). These little guys are really underated and the prices on the normal color ranges are really affordable (setup is pretty simple and inexpensive, too). The Isabels are what everyone wants - they're just so striking in color with the darker shades on white that you can't help but want one (it was a picture of an Isabel in Jerry Conway's article in Reptiles magazine back in Oct. 98 that sparked my interest in these guys). As more people keep these little boas and learn to breed and raise them, you'll see more of the Isabels offered. Not to mention all the natural color variance combined with their small size just makes them so attractive - none of my 5 are exactly the same color and all of them will stay within an easily managable size. They're just about the perfect pet boa...can you tell I'm slightly biased? 
Raven