How to compare nodes of different types but same fields?
I would create a custom field handler. This gives you full PHP power about how the link of the "find flats" button will look like.

Writing your own handlers for views maybe looks difficult at the beginning. Once you understand it you will use it a lot. Here I found a how to about how to do that (it's for views 2). You'll find a lot of real world examples in all modules that do support views. Look for code like MYMODULE_views_handlers .