A great many people do MEI for the time, as well as buy it in cheaper multis (i.e. Apache), from what I've seen.

As far as the King Airs go, I was able to fly right seat in a King Air 90 (no type req'd), and actually got to fly the empty legs, so that time that I was manipulating the controls actually counted towards multi-turbine-PIC (Part 91 operation). Like APM said, the 135 stuff gets a lot more tricky.

I think one should do everything they can to hunt down the multi for that first 100, forgoing opportunities that will build you more total, but no multi time.

My breakdown of multi, prior to being hired at a regional:

ME rating: 10 hours (Baron 58)
MEI rating: 8 hours (Apache 160)
My college's transportation program (all students guaranteed 20 hours): 32 hours (Citation Jet and King Air 90)
Weather modification: 49 hours (Baron 55)
Internship with a/c manufacturer: 147 hours (1900, King Air 350 and 200, Premier I)

Just keep chasing it down. As you can see, you might have to do some screwy things/move around a bit, but every 10 hours makes you that much more marketable for something bigger and better. As the previous poster said, just make sure you can back up everything you log with the regs.

Good luck!