It is only cheap if you put zero cost on your time. If you put a
realistic charge on your time for someone familiar with windows and
unfamiliar with linux then a few hours struggling with a new operating
system is going to exceed any software charges. This ignores issues of
usability, reliability and support which, at this point in time, are
almost certain to favour commercial programs.

Where open source audio software really wins is for people who
want/need to be more than passive users. Lots of academics and
scientists use unix-type operating systems for audio applications and
the available software is growing. Whether commercial grade support
will be available is another matter of course.

The best compromise to my mind is Mac OSX which has plenty of
commercial programs but can also compile and run almost all linux
programs. This enables open unix programs and commercial programs to
run side by side without any penalty apart from the slightly higher
hardware costs.