What is a fair price for permanently giving up a piece of the only brain you're ever going to have in your career in exchange for a job from which you can be laid off at a moment's notice without, it must be noted, getting back that piece of your brain you had to sign away?
If I were (which I am not) gullible enough to buy into the kind of rules that applies the same logic to ideas as fixed property [1] I would certainly start the conversation by asking what kind of rental you think you can afford!
[1] ...and then everyone acts surprised when both the market for ideas and fixed property suffers!