Let's get some terminology straight:
The "lever" is a small piece that your fingers wrap around. It has a hinge point and a cable attachment point.
The lever attaches to the "perch" which clamps to the handlbars.
The lever has to match the perch. Most of the cable ends are the same, so you can buy a "universal" perch (with lever) and intall it on almost any bike.
Other than the fit, there are other differences in the levers. Specifically, the material they are made of. The less expensive levers are made of a less expensive material that is brittle, and they break when get an impact. The more expensive levers are made of a material that can bend, so when you drop your bike you end up with a custom bent lever instead of no lever.
Where do you live that has only one store that doesn't carry levers?
I have broken so many levers I have taken to carrying spare levers (both brake and clutch) in my spares box. I recently broke my clutch lever 9 miles into a 20 mile loop of an enduro and had to ride 11 miles without a clutch. After that I did just what jdager said, I bought the ASV "factory seconds" levers. Note that the ASV clutch perch was a "universal", should fit any bike.
Rod