change of central heating boiler?

My Potterton Electronic neataheat 16-22 has to be changed as spares are scarce according to the service engineer from British gas. He said you might be lucky with a museum. £3420.50 before discounts was quoted. £2822.76 after discounts. Does this sound a fair price? open easily access boiler [no cupboards]. Oh It is possible the pump will need changing but B.G would charge extra as it wasn't included.
2nd choice.[not quoted for]
To change to combi boiler [ Green in mind] so we can remove the header and hotwater storgage tanks what would that likely cost be?