Google, Dynon and probably others are offering low-cost instruments such as this one for the Experimental market:
https://buy.garmin.com/en-US/US/prod514383.html
Since the G5 includes attitude information it would be illegal under current rules to take it to a glider contest, but... What we have here in a very compact 3 1/8" space is all the flight data you need including airspeed, altitude, heading information, vertical speed and slip/skid. The built-in GPS will indicate ground speed and of course you have attitude info. I wonder if this would satisfy regulations as a stand-alone basic instrument. You would only have to add a vario, flight computer, radio and transponder (PFlarm integrated in moving map) for a very compact panel. Redundant altitude info would come from the vario/gsp which also today often displays airspeed if so desired.
With back-up batteries, what could go wrong?
Herb