Has anyone tried any of various AOA instruments on the market?
There are
several under $1000.

Except, there's no need for a separate probe, just use the glider's
nose as a probe's nose cone and add the pressure sensing ports.

If you are looking for a simple DIY AoA indicator you might want to
check http://www.akaflieg.tugraz.at/akagproj.html
Parts cost around $20, and you can build it in an evening. The
downside is that there is no good integration with XCSoar yet, but
that might change if there is enough interest.

Michael