Accessible Cars

Why, oh why must accessible cars cost so much?  We have a 2001 Dodge Grand Caravan IMS conversion that we purchased new.  Needless to say, this has been our primary family car for nearly 10 years now, and it is in desperate need of replacement.  The door has never quite worked properly; and in this cold Utah weather, it certainly hasnn't gotten any better.  Our goal is to try and make this one last as long as possible, praying that the engine won't give out on us after 146,000 miles.  Then, we would like to try and pay CASH for the next one.  Now, we are not a rich family, so this feat of saving around $50,000 is going to take a lot of time, energy and discipline.  Anyone have any ideas on how to cut the costs?  Buying used is not an option - they usually have high mileage and are not very cost effective...  I have thought about purchasing from a company that converts used cars after market, but I honestly don't think that the quality of the conversion is as good as the vehicles that are converted as new.  Is there any assistance out there for purchase that I don't know about?