Depends on who's selling them.

Depends if they have cones with them or not.
Depends on the kind of cone.
Depends if they work.

I've seen people ask anywhere between $20 and $25 for a pair without cones. I don't know if they actually sell at those asking prices though.
The cheap way to get them is to find auctions that sell complete control panels, with those buttons on them. I scored 2 for $1.99 this way.
~Ray