But, from the core rules, a ritual can be used to create a Magical being using a ritual. This has been confirmed in Hermetic Projects. Many mystery virtues are extremely powerful. They all do crazy stuff. Bind Magic Beasts is just one of them.
Plus, for any magus to keep a Might 60 Creature in their lab, they need some serious magical power. Circular Ward against Magical beasts lvl 60, Penetration 60.
Any magus senior enough to do this sort of thing has any number of ways to earn vis. They could be a longevity ritual specialist and get paid 40 or 50 pawns per season for the best LRs in the Order.