My formula -
Field touch-ups: File (freehand), but I usually just swap chains
Regular sharpening: Oregon grinder (round-filed), file (square-filed)
Rakers: File (freehand), while mounted in grinder.
I've been able to get a lot of use out of chains this way. With the top filed back to 20% of its original length and with the rakers properly lowered, chains sure cut quickly! And you can really get your money worth that way. Those not wanting to do it freehand (which works better for some chains than others, Oregon is particularly amenable to hand filing freehand) can get bar-mount clamp/guides, bench-mount clamp/guides (Stihl makes one that is great), or electric grinders. The NorthernTool (and now Bailey's) Chinese clone of the Oregon 511/Tecomec 136 is a decent value for $100, and with a bit of cleaning up of casting debris, poor finish, and some good wheels, it can produce great results. The actual Oregon (Tecomec, SpeedSharp) or MAXX grinders are great, too, especially if you have lots of chains to sharpen.
I agree that some chain types/lengths are cheap. But others, like the 135 drive link loops on my 42" bar, or 60" of .404, represent a significant investment per loop. Even the short ones cost money, and given that a nicely sharpened chain cuts better (often much better) than a new loop, it seems a waste to toss chains after they get used, or even after getting rocked out. And if you need unusual angles or do something that requires regular sharpening (milling, for example, where you're sharpening ever couple passes), getting skilled with a file or a grinder is a must.
The other thing that always comes up in sharpening threads is the cost of sharpening. A $7 sharpening job can be a steal or a waste, depending on who sharpens and how. In high school, I worked at a hardware store where I did all the sharpening, because I was the only one who knew anything about saws. Looking back, my work wasn't that good, but the stuff that the other employees and owner did was terrible. Some of the local saw shops will sharpen at 10c/drive link, and the results are impressive. As with most everything else in life, $$ is only half of the story...