Java APIs

I recommended use of javadoc for documenting code in a new project; then heard the whole system will be constructed in a variety of languages, including C++ and possibly some C# (and Java ... I wrote as though that was assumed).

So now I'm asked to find a tool that produces javadoc results automatically from comments in all source code, regardless of language. And, one more thing ... javadoc is free ... so nothing was added to the budget for a documentation tool.

Thanks if you can tip me off to a solution.