I would ask Dell to give you the part number for the motherboard (Intel GX87... or whatever) and then contact the motherboard manufacturer directly. The motherboard manufacturer would know better than the chowderheads at Dell whether you'll be able to run 2 monitors.

I recently bought a computer and had a small, local company build it. I was able to ugrade to a motherboard with 2 PCI Express slots for something like $50 to $100 extra. That might be something to look into.

Also, check techbargains.com for Dell coupons. You might find a better deal than the one you currently have.