Those are typical prices for BRB's, they've settled around $100 - $150 for babies and $200 - $300 for adults. That's for typical BRB's. Brighter cleaner animals will command a higher price.
IMO babies ar ethe way to go, you'll rarely find an extreme adult for sale, while high end babies are available every year. If you do find a high end adult for a reasonable price, snap it up. Beware of WC though, those "can" be problematic. And should have a vet check which will raise the actual cost significantly.
Adult females would be most readily purchased after breeding season when breeders such as myself are replacing a more normal one with a higher end female.
All that said, I bought this one as an adult, not well cared for. Has not bee a great breeder (one ok size litter in two years) but her babies are outstanding. This is year three and looks like she may be gravid
Savannah:

This one was bought as a baby and looks to be gravid for her first time this year:
Daisey:

I also had the opportunity to purchase a trio from Howard, the breeder who produced Daisey including her parents. He didn't know which female produced her but since I have both, no biggee. These opportunities are few and far between.
Fred, Wilma and Betty



My only other adult purchase was a very special one. A WC gravid female dropped a small litter of 8 babies. In it was the wildest looking striped hypo baby I've ever seen. I bought the entire group, mom and 8 babies. A fresh hypo line and a possible one of a kind stripe line.
Eve the WC female and Genevieve, the striped hypo:


Lastly, if you want to produce "off the chart beautiful" babies, IMO you would be better off starting with "off the chart beautiful" parents. IMO, the babies colors will be in a typical bell curve distribution with the mean being the average of the parents. The higher the average color of the parents, the higher the average color of the babies AND the higher the top end of the curve goes!!
So if you're in a hurry to produce some babies, go with adults. If you want to produce screamers, then only buy screamers. Typically babies but if you come across a screamer adult then go for it!! I myself have paid 2x "normal" prices for the right baby. If you're really serious about getting screamers then get on breeders wait lists so you'll be higher in the picking order.
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Thanks,
Dave Colling

www.rainbows-r-us-reptiles.com
0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)
LOL, to many snakes to list, last count:
20.28 BRB
16.18 BCI
And those are only the breeders 
lots.lots.lots feeder mice and rats 