Having bought Modern Backdrops, I can confidently say it'd be useful for you running Shadow Chasers. It's not just maps; it has adventure hooks and sample enemies for a variety of different levels.
I'd consider starting with the sample Shadow Chasers adventure in the main book (with the zombie on the bus), then one or two of the free low-level adventures off Wizards' site, then link in some of the Modern Backdrops bits.
Also, Dark*Matter is only $5 on rpgnow.com, and while you'd have to do conversions of the material, there's a conversion article on Wizards as well. I think "Exit 23" is a great introduction for a Shadow Chasers style campaign, personally; just play up the mystical side of things and downplay the X-Files stuff.