96 Mercury Villager/Head Gasket

We just bought a 1996 Mercury Villager with 105,518 miles. Milage now is 105,584 with a 3.0 engine. I had the oil changed at Wal-Mart on a Monday, drove it to and from work until Friday. My husband had it all day Saturday. He said it just quit on him going down the road. He re started it and got it to a friend's house. He towed it home on Sunday. Monday I take a look at it and there's no oil in it at all. The bottom of the van has oil everywhere. I put a quart in it so I can hear what it sounds like. I start it and it sounds rough; as if there is all kinds of air going through it. I guess I need to know if you can tell me if it is a head gasket, how much it would be with parts and labor and if I should replace all the seals while it's being worked on. Because the fact is, the dealer that I got it from got it from a bigger car dealer and I really don't know how long it sat without being started. I would really appreciate your help. I'm about 7 mo. Pregnant and mechanincs always try to con me out of money, and my husband doesn't know as much as I do aobut cars, so he never remembers what to ask.