It really depends on a lot of things, where you are, condition of the vehicle, condition of the engine, anything that needs either to start is not in good condition, there could be a lot of things that cause this also, I have a rig that no matter how long I turn it over it will not start, it turned out to be electrical, specifically the oil pressure circuit, these trucks need oil pressure before the injection pump controller will move to the start or run position, I changed that sensor and nothing improved, but if I removed the wire from the sensor it starts right away, after I figured that out I changed every electrical component and there was still no improvement, so now I just leave that wire off the sensor, I still don't know why it will not work properly to this day, I have an oil pressure gauge.
Using ether is bad for these engines, very bad from what I have heard, I don't know that I would buy a rig from someone that instead of fixing the issue they use ether to get it going, makes me think they have not a clue what is going on, I suppose if it was cheap enough that I might buy it as a parts rig, and then if you can figure out the issue you will be ahead, but it is not a running rig if you cannot get in it, turn the key on, let the glow plugs warm and when the light goes out start it, and when I want to shut it down just turn the key off, anything else is not a properly functioning rig.
So around here in the Pacific Northwest a diesel rig that functions properly can go for under a couple thousand or more, ones that need special needs go for under a thousand, I have bought several diesel trucks that the engine started without issues to the surprise of the owner for $500.00, but they had to be towed home because the transmission was broken, they had no brakes, or they were literally rusting away, I have brought home several $500.00 dollar trucks and fixed them.
Recently I seen an ad for a diesel truck in Portland for $2000.00/$2050.00/$2200.00, unless that truck is in awesome shape I would not pay $2000.00 for it, but that is me, this is the ad for the one I am talking about, the guy has 3 different prices in 2 different ads.
https://portland.craigslist.org/wsc/cto/6066932199.html
I have never had a diesel truck that got over 35mpg, but I drive fast on the hiways, a friends dad had a diesel 720 that he said got 41mpg, but the guy drives 50mph every where, he has the lightest foot I ever seen, he is aggravating to follow, he may have got that type of mileage, that engine ran real good.
Another thing I would be suspect of is if the engine is warmed up before you get there, when I used to go look at diesel trucks I told them not to warm it up before I got there, I said I wanted to be the one to start it up, it had to be overnight cold, fact is I have never paid more than 2000.00 for a diesel truck, and that one was perfect, it had a rebuilt engine in it and a nice contractors canopy, it was a nice truck.
If your in the Portland area, are you the one that called me about my Nissan diesel parts ad, but you were looking for a complete truck?