Has anyone seen compound parabolic panel solar collectors?   They use a specially shaped trough to focus the heat  directly onto a pipe (no flat sheet needed), but do not need to track the sun like a normal parabolic.   It would seem that these could be CNC hot wire cut from blocks of foam and then covered with a reflective film to produce a very low cost  collector for hot water heating.    Glass over the top is optional.

http://www.fossilfreedom.com/increase-output.html
http://home.att.net/~cleardomesolar/solarflex.html

There's at least one commercial product based on the Roland Winston patent that bears his name:

http://www.solargenixchicago.com/cpccollector.cfm

http://www.solargenix.com/pdf/CPC_CollectorInstallManual.pdf

http://chronicle.uchicago.edu/040415/winston.shtml