How much have you spent making your house energy efficient?

With energy prices still high and the EPC regulations tightening, I'm thinking about investing in energy efficiency for our 1930s semi. Currently rated EPC D.

Got some quotes:
- Loft insulation top-up: £400
- Cavity wall insulation: £1,200
- Double glazing (replacing original single glazing): £8,500
- Air source heat pump: £12,000 (after BUS grant)
- Solar panels (4kW): £6,500

That's nearly £29k to do everything. My energy bill is about £2,200/year. Even if I halved it, the payback period is 26 years.

What have other people done? What's actually worth the investment vs what's "nice to have"?