Bought Vehicle(w/ financing), got messed around...?

So, we swapped in our old 1995 vehicle for a brand new 2007 vehicle. Now of coarse there is financing involved as our 1995 vehicle was not the most expensive vehicle. So we got a measly 5,000 for it because my husband said thats all he wanted and the dealership jumped at it. So, moving on. The new vehicle had a worth of $50,000. So $5,000 was knocked off. That leaves $45,000 owing roughly. Husband then started signing papers WITHOUT reading them first. I noticed shortly afterwards when we were driving home in our new vehicle, that our last payment amount would be $12,500... Does this sound right to you?? I mean we BOUGHT the vehicle we are not leasing it. Please if you have any info on this, that would be great!!! Thanks!!