Col-the lowest grade of commercial ether is perfectly adequate for our usage-that is 'solvent grade'. from chemical supply firms ether is normally available as 'solvent' (generally in the larger quantities-20-litre or 200 litre drums), next up in purity comes 'GPR'-general purpose reagent for general lab use, than 'AR' standing for 'analytical reagent', then 'spectral grade' for UV or visible spectroscopy grade and finally the ultra pure HPLC grades-with each ascending level obviously the impurities go down and the price goes up!
AS regards 'anhydrous' well ether is not especially miscivle with water, and does not absorb water in the way that methanol or acetone or some other solvents do. So even normal ether has a very low water content-but there are some synthetic or laboratory reactions for which even a trace of water is undesirable, so anhydrous ether is available (at a higher cost, since it requires an additional treatment) for such critical applications.
For our diesel use, traces of water at a few tenths of a percent are irrelevant-it doesn't affect our engine running in the slightest-and diesel fuel does not absorb moisture, unlike glow fuel. If you've never done it, you will find that a 'drowned ' diesel will start and run even with quite a lot of water still inside-the exhaust residue is white and emulsion like for a few seconds until it clears the water out-but even a unplanned dunking-landing in a pond or nosing over on takeoff for a waterplane, does little harm.
In short-by the cheapest grade you can get your hands on-any grade of ether will work for our purposes-and your decision should be based on availability and cost-per-volume considerations rather than chemical purity. [ie-you might find a 20-litre drum the most cost effective option if there are several of you] I don't know if Ajax Chemicals are still in business on Oz-but they were very competitive when I was buying ether for the Dunedin MAC about 15 years ago-though of course I was dealing with the NZ subsidiary then.

ChrisM
'ffkiwi'