Just to manage expectations, I doubt you’ll ever get it for £3k unless the grant is significantly increased.
Half the cost is labour and that’s only going to go up. Heat pumps themselves are not getting cheaper because they already benefit from economies of scale.
The only benefit it’s potentially from competition and the race to the bottom. As it stands, other installers seem to be letting Octopus crack on with that - just look at the prices
@Ron-ski is getting for and easy install with no radiator changes.
If the government move the green levies from electricity to gas, that may change the game mind.