No, there is no free version of expression blend (apart from the time limited trial), and there hasn't been any announcement of anything planned.
Several useful tools are:
Kaxaml and XAMLpad for testing blocks of XAML.
StyleSnooper allows you to grab the default styles/templates from all the existing controls in the framework. Very useful if you just want to modify an existing style or template a litte.
Also, reflector has a BAML plugin available which can come in handy at times.
We have expression blend (as part of an MSDN subscription) and we barely use it. We used to use it for 2 things. 1) To grab styles, we now just use style snooper, it's easier. 2) For testing custom templates of complex controls like list views, we have now re factored the architecture slightly to generate test data when the XAML is being displayed in visual studio so we don't have to switch to blend all the time.