This is a good idea. Doesn't work for people on visas but I can imagine working this out somehow. Basically, make the potential employer realize that your time isn't free.
I don't really agree - I remembered a take home assignment which combined enterprise-like object-oriented design (data model, strategy) with algorithmic thinking (several flavors of graph traversal). The job also turned out to be top-notch before the company was bought by a certain trading firm which has 2/5 (and falling) on glassdoor. 9 months later it was pure shite. it was the best team i ever worked in though - still keep in touch with some of the guys :)