I think it might have worked if, like others have said, the Johnson didn't set them on one specific plan. If he laid out the premise, and then said something like, "I can get a few of you in as guards, but the rest of you will have to pose as other prisoners. I'm open to other suggestions." That would have given the runners some control over the run. The run, as it was, was completely in the hands of fate (aka, the GM).
Also, the reward should most certainly have been much higher. Even in a medium/minimum security prison, being caught means being branded with a Criminal SIN and anywhere between 6 months and several years of imprisonment. Oh, and if you're full of 'ware, it all gets painfully pulled out of you (and there goes all your nuyen investment). If you're magical, you get branded as "dangerous" and moved to a much higher security facility, with a longer time in prison. They won't get to use any of their powers, either being put into mystical cuffs/mystical jackets or just sat right on top of a mana void. Neither of which is a very pleasant (in fact, it's rather tortuous) experience.
So, yeah; the offer should have come in at about 30k up front, with probably another 30-40k after the objective is secured. Leaving some room for negotiation, too.