You should start with whomever you buy your alfalfa cubes from. Are you buying them locally or are they being trucked up to you by the pallet? If you have a "local" feed store, who are they buying from? Get their name and # and call them up (even the smallest mills typically have a nutritionist). Explain your situation and see what they can come up with. I'm sure your dilemma is not unique up there. Throw out extruded as it's a more sophisticated milling process and stick with pelleted. Only the largest mills can make extruded feed. Pellets will also be cheaper. The pellets can range from rabbit chow size up to horse cookie size. The larger they can be made, the less waste you will have because less is left on the ground. If you think better metric, you want a pellet with a diameter of 15-20mm.
Let's just say you feed 3/4 alfalfa cubes and 1/4 oats.
If you fed 300# alfalfa cubes, that would provide 300Mcals. (1# of alfalfa has approximately 1000kcal or 1 Mcal).
100# of oats would provide 130Mcals. (1# of oats has approximately 1.3Mcals).
300# of alfalfa cubes + 100# oats will provide 430 Mcals.
A typical Senior feed has about 1.5 Mcals/#. To get those same 430Mcals, you would need to feed 287# of senior.
From a transportation stance, that's a savings of 123#. Now that's not the whole picture as I would not totally eliminate the cubes from the diet as you want some type of long stem forage for them to chew on and help with digestion but you can see where I'm going.
Can the mill that makes the cubes add oil to the binding agent? Adding 5% oil will increase the caloric value to 1.15Mcal/#. It's not going to increase the volume you transport but now you've managed to add a few more calories. A small mill is not going to want to lose your business and if you're talking 10+T of product it's so worth their while to work with you. What's a batch size for them? That will probably be what they want to make in a run.