You might want to check out the Dynon D2 at their website (http://dynonavionics.com/docs/PocketPanel.html). At $1095, this is NOT a certified piece of equipment, and cannot be "permanently" installed without an STC (which you would not find easy to get), but comes with a spring-loaded mount that clips very securely into a standard 3 1/8" panel hole, so you don't have to bother with any paperwork. Of course, you cannot legally use it to replace any existing instruments, nor use it for intentional IFR. But I know several CFIIs who say it is amazingly good - maybe even more accurate and responsive than traditional vacuum-based AIs...
It is based on the same MEMS technology (solid state, no moving parts "gyro") used in their experimental panel systems (Dynon Skyview EFIS), and provides GPS-derived altitude and ground speed (not airspeed!), along with heading and attitude information.
Alternative #2 would be an iPad Mini and a Stratus 2 or 2S, with either the free Status Horizon app that basically duplicates the same capabilities as the Dynon D2 above, or the "not-free" ForeFlight EFB app, which includes the same functionality as the "Stratus Horizon" app, embedded within ForeFlight.
Any if these will provide excellent emergency situational awareness capability, and could save your bacon in a "VFR into IMC" situation.
Note that I am NOT advocating these as a replacement for IFR equipment - they are NOT certified for that purpose. Nor am I advocating using their capabilities to push on into IMC without an IR and the proper IFR equipment - that's just dumb!