Is Boa Constructor free/open source?
Yes. There is no charge to download and use Boa Constructor. (See Downloads page)
Can I migrate existing graphics-based wxpython program into Boa Constructor?
No. Boa Constructor creates code in a specific format and expects this format to be present when it's updating the code.
It is not a trivial task to do the conversion but building a convertor may become task some time in the future, depending on demand.