Dilemma

I like my car.  It is good on gas, and it typically gets me where I am going with a minimal amount of hassle.  I even think my car is nice looking.  I like it's pretty blue colour.

About a year ago I noticed a small spot of rust just behind the rear wheel well on the driver's side.  Over the last year it has grown quite a bit.  Now the rust has bubbled up from underneath and it is starting on the other side as well.  A few months ago I went to an auto body shop just to ask about the cost of having it fixed.  I was told that because the rust was all the way through the metal, that the rust would have to be cut out and they would have to weld in a new piece of metal and paint, etc.  All to the tune of about $2500.  That sounded crazy at the time! 

So after a quick trip to the Mazda dealership today, we found out that our used car came from Ontario (though we were both pretty sure that we were told Alberta when we bought it...).  So basically we are stuck with a prematurely rusting car due to the fact that they like to use a lot of salt on the roads in Ontario.

So here's the dilemma.  Do we sell the car and get what we can for it while the rust is still fairly minimal.  Or do I drive it until it won't go anymore and it is worth nothing, then start over?  I am not sure what we could get for a trade in value for it.  I don't know how much this bit of rust would be a detriment to the value.  Or would we be able to get a decent dollar for it if we try to sell it privately.  I know that if I were looking to buy a car I don't think I would be too thrilled with a car that is showing signs of rust.  Especially a car that is only 7 years old.  Ugh!  I had also thought about fixing the rust then getting rid of the car, because then we might be able to get a decent value.  Though I am not sure we would regain the value lost because of the rust, if we were to fix it.  *sigh*  Any thoughts?