The price makes no difference whatsoever. It could be great or it could be terrible. The only thing that matters is the attitude of the girls and how well they work together.
I wouldn't chance it with an agency I wasn't familiar with, or where I hadn't seen at least one of the girls solo before, preferably both. That would give me the best idea of how they might get on.
As usual, YMMV, but I've had a lot of exceptional duo's by sticking to those rules.