The price difference for the Garmin G5 is a bit of a ripoff, but not quite as much as mentioned above.
https://www.ozpilot.com.au/garmin-g5-system
I've been looking at the G5 too, and will probably get one next time money needs to be spent on vacuum powered gyros in my plane.
If the Avionics LAME will do the installation based only on the STC it's probably the best option as EOs cost time and money. If your plane is NVFR or IFR the certified option might be your only choice.
I'm hoping in six months time the G5 certified price will soften and I'll wait for a good deal to pop up.