$20 for pullets is a fair price. 
I brooded 150 chicks last year and my electric bill went up $400 for the two months because I had 4 heat lamps going.   If you buy chicks for $2.50 and then figure time, quality feed, ELECTRICITY and clean bedding for 8 weeks you are pretty close to the $20, and all the hard work and most of the risk and is done. 
I have heard horror stories about sellers on Craigslist who were selling sick pullets that were infected people entire flock when they brought them home.  It is vital to get your birds from a reputable facility that cares about the health of the birds and who will be open and honest if their birds have been exposed to or are carriers of any diseases.   
I have not met Rachael or seen her farm, but I know someone who used to keep their horse there and I understand it is a top rate facility, and if I were in the market for pullets, I would not think twice about buying a True North Pullet.
If money is an issue, then you should really consider getting chicks.  They may end up costing about the same amount of money in the long run, but at least you can spread the payment out over the 8 week period.