Roland Christen discussed the differenced on the AP Users Group:
"In general, there are 4 things that set the cost of an eyepiece:
1. degree of polish
2. type of coating
3. length of production run
4. size of the glass
I will deal with each in turn.
1. polish for twice as long, minimum, as it takes to get the grey out, that is the rule of thumb in the industry for a good deep polish. This is the Zeiss standard, and they don't deviate from it. Take twice as long, costs twice as much. You can see where it is possible to shave off some cost. A manufacturer will say, lessee if they'll notice if we only go 50% longer? NA! They'll never know the difference. Lessee if they will notice if we only go 25% as long? NA! they'll never see the difference. Lessee if ... etc. No, they'll never see the difference, BUT you will be celebrated all day long and praised for offering the eyepiece for LESS MONEY, right?
Is it necessary to polish for twice as long? The answer is yes, since below the fine ground surface is a thin layer of subsurface damage that cannot be seen, but shows up later after the glass undergoes the coating process where it gets heated to 600 DegF. It puts ever so slight haze into the optical path.
2. Most eyepieces, including most premium eyepieces, do not have an efficient multi-coating on all surfaces, and some are only multicoated on one surface. It goes like this - as the lenses come off the production line, they are multi-coated on production coating machines, without regard to glass type or index. This results in a nice rainbow of colors (reinforces in the purchaser's mind that, by golly, I got a real multicoated eyepiece here). Unfortunately, that rainbow tells me right away that the coatings are not optimal, just average, and, believe it or not, sometimes thay can be worse than no coating at all. Zeiss coats each glass according to it's own unique index value. It requires constant monitoring by skilled technicians, as well as adjusting the formula. The other thing is the type of evaporant that is used. Some produce a so-so coating, other, more expensive materials produce a very high transmission coating. High index glass is the hardest to coat properly, it wants 4 or even 5 layers, whereas pretty much all the popular eyepieces I've seen use typically 3 layers, or even only one layer for very high index flint elements. This results in a yellowish tint to the image, and a blueish glow coming out of the eyepiece.