My LS seems to use approximately 1.5 gallons of diesel per hour so at $3 per gallon that’s nearly $5 per hour just for fuel alone.
I have the 40 HP version and I go through about 1 gal/hr. But I have never really tracked it so just a guess. I put on about 100 hours a year, doing things that need doing, so I do not worry about the cost of fuel. It costs me more just to have it sitting there with all that cash tied up.
It is break-even "investment" for me. With the money I save, and the value of barter work I do for neighbors/friends it is worth keeping for now.
I love comments like "I don't care". That tells me the person has to have a tractor, or someone who has a toy and enough money to afford it. I suspect there are a lot of folks who wind up with a toy after 2-3 years, and most of their tractor projects are done. Others find projects to do to justify keeping the machine. Nothing wrong with either mind set.
In any case, fuel is a minor component of operating costs. Saving less than a gallon an hour on a machine that struggles to get work done is a silly thing to consider if, like most hobby users, you put 70-100 hours on a tractor. The more capable machine will do some jobs faster and more importantly, a lot more safely. 100 hours at .7 gph is the same as 70 hours at 1 gph.
I could have saved $2000 by getting a 35 HP 3000 series instead of the 40 HP 4000 series LS. That $2000 difference got me a tractor with 5 more HP, that is 800 lbs heavier and lifts over 500 lbs more at the FEL, 900 lbs more at the 3PH and is more stable. If that costs me another .3 GPH I don't care.