What could be making my car do this?

I have a 2001 Mercury Villager. For the last week or so it has started to sputter and jerk when I'm going uphill. Today, it started doing it the whole time that I was driving, so I thought that it could be either the fuel filter or the spark plugs or wires. Well, my speedometer started going up and down at random and the whole thing sputtered to a stop and wouldn't go any further. What could have caused this? Is this going to be an expensive repair?