I know its the premise of the movie, but...

He really had no alternative?

CIA agent comes to you and says "You have to do this dangerous mission. The risk is indefinite imprisonment in East Germany or worse. Otherwise, your research funding will be cut."

I know its the premise of the movie, but it just seems ridiculous the CIA's only possible solution to its problem is this random professor.

At the very *least*, he should be able to negotiate a substantial payment, taking into account the substantial risk he is taking. But, No, he just shrugs and goes and does it, for free.

Plus, from the very first, he's alerted (for some reason) by the East Germans that they know exactly why he's there! Any normal agent would immediately bug out from there knowing the mission was blown.