Selecting the right keywords ?

[nRnF]

I own many very general domains names with traffic, and I relly have
difficulties to choose some generic (high paying) keywords.

Is there any tool, that helps to set up/selecting PPC keywords.

I am looking for a function where you introduce a keyword, and in teturn it shows
the avg. PPC and some related keywords with av. PPC.

Or you introduce a category, and the tool returns some word suggestions with av. PPC.

I know, that indication the av. PPC is a bit tricky, as this varies within PPC providers.

But I think you got the idea what I am looking for.

Any suggestions are highly appreciated.

How do you select your keywords ?