In this particular case I'm not talking about grabbing random people, I'm talking about people who are very skilled in a similar tech stack (which has a much higher supply/demand ratio, and getting them up to speed with the very similar but niche stack. Basically you're just learning some new APIs and some new service providers (i.e. proprietary ORM instead of Hibernate).
But I agree with your assessment of consulting firms and the scaling/quality issues therein. I also feel that consulting shops expenses tend to scale a lot closer to profits than some other businesses, so I stay out of it:)