OK, after crunching some numbers, either the Ford dealer is seriously hosing you, or there is something wrong in this equation.
I looked up a VW Jetta TDI, with no options (it is pretty well equiped to begin with) you'd probably pay say 22 grand. Even with rolling in 6 grand of negative equity on the van (which you could probably reduce somewhat, if you sold it yourself and then covered the diff in cash, assuming you have the cash), that 28k financed over 60 months, at 5.95APR (the 60 month new car rate from USAA) works out to $538/mo which isn't awful, but isn't cheap either.
Just something else to think about.
