A lot of the cost depends on what manufacturer you go for, installation costs tend to be the same regardless - assuming a 'normal' installation. Our panels are on the garage which is 30m from the house so we needed a lot of armoured cable and Cat6 to be laid which pushed the costs up quite a bit, the installers reckoned it took them twice as long as normal to do our system.
For the installation we went for 12 x 400W Sunpower panels, a 5KW Solar Edge Inverter, 7.5kW LG LiPo Battery, ZigBee IoT controller to switch remote devices and a Zappi charger. Total cost was around £17k.
It produces around 3MWh/year of electricity we can use, so at 50p/KWh that's about £1500/year saved. As the electricity price increases I would expect the payback period to drop below the 10 year mark.
The only thing I regret about our installation is that I should have gone all-out and bought the decoupler kit that allows you to continue to generate and use solar power when the gris is shut down. It seemed a remote possibility a couple of years ago, and was a significant additional cost so we didn't go for it, but with the benefit of hindsight...
The only advice I would give anyone is to go for a reputable installer and buy decent kit, especially with regard to support and guarantees. As with everything, it might not be true that you always get what you pay for, but it is always true that you don't get what you don't pay for.
