STC value for money
The suggestion from another Aspen dealer is that use of the STCs produced by Lees and others (Tatenhill have the PA24 and FR182, Straubing in Germany will soon have C172) will be around €600. That's much lower than the cost of producing the STC in the first place, so clearly the avionic shops that have gone to the bother have made a significant investment and need to recover that cost.
Aspen and Garmin have both certified their prodicts in Europe - they have ETSOs, so it's not their fault that EASA doesn't accept FAA STCs. And you can't really blame EASA when not automatically accepting everything the FAA does. Look at the fiasco with the Eclipse 500, which EASA wouldn't accept initially. If it had a double generator failure (and this is a failure case in both FAA and EASA certification requirements), it would have run out of battery power and had NO engine control long before it could have completed an emergency descent in IMC. It has no manual engine controls, including firewall shut-off valve. EASA made them fit a different battery to meet the required 60 minutes. Seems rather sensible to me.