I have a 2000 Chevy Suburban and a 2002 Mazda 626. Betty loves Mazda's. She had a 91 Protégé that we gave to my niece last year because we had no where to keep it and it was basically rusting. At that time it had 253,000 miles on it. In September it hit 290,000 and is still running great. It looks like hell but it runs great.
It has never had any major mechanical problems.
Betty's 626 has 102,000 on it and other than the distributor from hell it runs quite well. My Suburban has less miles and runs well but it's more of a utility. Betty has given up on it after the last hunting trip.
I like your idea of the diesel. Just by new! Many older diesel engines do not run well on the bio diesel and clean diesel mixtures. Also hope diesel prices come down!