Which in this Quest is the reason why we didn't have the option to spare the Skaven Breeders - they were mutated enough that they wouldn't actually be able to survive without a warpstone infused diet to keep their bodies functioning, and that something we wouldn't be able to provide.
Now in all fairness if we had more time we could have tried to jury rig a Dhar infusing array that could create warpstone but the middle of a battle, right before another battle really wasn't the time for it.
Then again there never seems to be time for this sort of experiments...
I wouldn't be surprised if the Grey College doesn't let someone else just blatantly pay your way, because of that whole pesky vow of Poverty and also as an early character test to see if people are going to try to cheat, and more importantly how.
Whilst the Colleges do shave off tuition for diligence money doesn't actually provide the means to cheat. You can't just buy magic talent with gold; at most you might be able to get better teachers and a staff - but even then the best teachers and best staves are going to be MLs - which can't be bought with money and can't be really stopped if they decide to favour an apprentice.