I almost did exactly what you are thinking about doing. I was prepared to drop about 7 grand to go through my Caravan initial so I might have a better chance with someone like MartinAir. I ended up getting on with AirNet instead. They put me through initial and checked me out in the Baron, then I bid to a Reserve pilot spot and ended up not only being sent to Caravan initial on their dime, but also checked in the Piper Navajo. Triple qualified, and there were many nights that I'd fly two of the three... and one night I did fly all three! I ended up with over three hundred hours in the 'Van over about a year and a half. Great airplane!! But... I'll never fly one again anywhere there's even a hint of ice. NEVER! Those two winters in the 'Van took about 5 years off my life!
My personal opinion... save your money. If you really want to fly the Caravan there are jobs out there... and they usually want to train you to their standards anyway. Try MartinAir at ADS in the Dallas area, AirNet at LCK in Columbus, Ohio or even Pacific Wings out in Maui, Hawaii. Slim chance of ever seeing any ice out there!!
Paul... by the way... is that a Tropic Air caravan in your avitar? I talked to their chief pilot a few years back... they wanted 1500TT with an ATP rating to get on with them flying around Belize. Looked like a sweet job!!