Question about purchasing a Mazda MPV?

So, after going back to graduate school, I find myself in need of a dependable vehicle for under $3000 (I know that's kind of an oxymoron). Nevertheless, I don't want to stretch myself so thin with paying for school and a car payment, I'd rather suffer a couple of years with an older car and hopefully it will pay off in the end. I've found a 2000 Mazda MPV for $2200 with 105,000 miles on it, which for that price and a ten year old car that's appears to be in decent shape that seems like a possible good deal. However, the owner says there is a slight miss in one of the cylinders and that spark plugs could fix this. After talking to my dad, he says that spark plugs are a fairly easy fix and if that's all that is wrong with the car why don't they just fix it? According to the seller, kids are no longer at home, they don't need a van and are just ready to get rid of it. So, what I'm wondering is, what else could be wrong with it? If it really is just the spark plugs that need to be fixed, would it be too unreasonable to ask they fix it prior to me buying it? I think it would make way more sense for them to spend a few bucks so that I feel good about my purchase rather than me buying a money pit. All thoughts and helpful opinions are welcomed, thank you!