I just drove from northern North Dakota to southern Arizona via SLC/Vega$ (in a diesel..). Fuel prices ranged from $1.70-$2.10 per US gallon, diesel $1.46-$1.80. So the comment about the fuel being cheaper are true, but not much of a change.
When and if someone were to convert a cruiser to diesel you must remember that a few models parts can be found. Canada used B, 3B (bigger 4 cylinders), and 2H (6 cylinder) models and if anyone cares the 2L and 2L-T (tiny 4 cylinders) in all of north america. Additionally, mines used 3BII's, 1PZ's, and both new and old 1HZ's. That being said, the parts for those models sits right now in 'japan north america' which is a big building in Ontario, California (basically LA for those w/o geography). In a pinch, you can also call a place like ENS Toyota/Lexus which is not only a dealer but also mine supplier and order most key parts same day (they are in Saskatoon, SK). (and a private comment, no 4 cylinder would work in a station wagon)
I don't even want to enter the speculation on why toyota are DA's about bringing in a diesel truck, but basically its all about money. They will not sell as many diesel trucks as they would need to support introducing parts to guys like Dan and educating mechanics and dealers. More key is bringing a product that lasts too long into a market where 3-5 years is max ownership (leases and 2 year trade offs). Diesels are young at 100,000 miles, resale of any car /truck in the US dies a rapid death at that number!!
Someone waaaay back noted cost of a "starter". 12V starter motors are all the same for diesels and a toyota reman 2L 12v is about $150. The front gear housings are different, but that does not stop swapping the electrical portion. A hell of a lot cheaper than a starter for a '95 Ford PS ($505 retail reman in Tucson 4 years ago).
...anyway, back to conversions. I think many here in the US would be disappointed by a 1HZ install into a heavy 80 series. It would be very slow relative to a 1FZ-FE and getting to highway speeds in areas with 75mph freeways would suck. So we jump to turbos (1HD-T, 12 valve 1990-1995, 1HD-FT 24 valve 1995-1998, 1HD-FTE 24 v all electronic 1998-pres). They don't take any form of US manual tranny, autos could be converted to fit but would cost more than finding the right one. 12 valves need big end bearings refeshed under the first 100K or they are dead (but these share many parts with the north america supplied 1HZ's). They are also 10 years old on average. -FT and FTE's do not have any parts supply in the US so finding crossover (via looking at parts books for hours) would be needed. FTE's are 8 wire 'drive by wire' engines so have fun making that one work. You want same day parts, you are calling Marv Specter and praying with your wallet.