I don't think $250 is unreasonable for a nice animal, especially if it is close to adult/breeding size. As for age, I have 5 adult boas and only 2 of those did I raise from newborns/juveniles. The other three I got within the last year to year and a half - two of them are roughly 4 years old and the other is around 7 years old. While a couple of them (who I got from the same guy) are not as accustomed to being handled as most of my collection is, they have calmed down considerably with gentle handling. The other one was dog tame when I got her and remains so. As for neonate prices, it depends on who you buy from and where you buy from. Obviously pet stores aren't the first choice, but most redtail boas (generally Colombian redtails but sometimes Central American) found there are in the $150-$180 range. At a reptile show you can expect to see prices ranging from $60-$100 for nice, normal babies. I would say about the same for online prices, then add shipping. Obviously, this isn't including anything other than normals. Once you delve into the land of morphs or animals bred for especially good coloring, the price goes up. FWIW, I've never hesitated to purchase or adopt adult animals. I've found the majority of them settle in nicely and make good pets.
Raven