I got my single levels at mouser.com
I don't know that they're the cheapest, but they have a ton of stuff and are fast. The only thing is that if you don't know exactly what you're looking for it takes a while to find stuff.
The power to tax, once conceded, has no limits; it contains until it destroys. I was not joking when I told them to dig into their own pouches. It may not be possible to do away with government — sometimes I think that government is an inescapable disease of human beings. But it may be possible to keep it small and starved and inoffensive — and can you think of a better way than by requiring the governors themselves to pay the costs of their antisocial hobby?
R. A. Heinlein