A plug in solar panel and microinverter at the local supermarket is about €1k/kW. 9kW of solar for €9k/£8k/$10.5k to power an average US car and an average US house.

Avearge US car does 13,000 miles a year needs about 4,500kWh, so €4500

An average US home uses 11kWh a day, or 4,000 kWh a year, that would be another €4000

US electric price is an average 17c per kWh. That's a 15% ROI.

I suspect the costs your quoting are mainly things like scaffolding and labour, and that's not going to get cheaper.

The panels themselves - ignoring inverter, install, etc, are $100 for a 400W panel [0]. To generate a whopping 16,000kWh a year -- 70% more than the average -- you'd need to spend $4k on panels. Even if panels were free, your quotes would still be obscene because tradesmen charge obscene amounts (or rather roofing work is just expensive)

[0] https://www.solartradesales.co.uk/aiko-neostar-2s-460w-n-typ...