I've just read in this months 'Period Living Magazine' an article where the journalist is going to remove their oil AGA and replace it with a new 13 Amp electric AGA with controllable heat – basically you switch it off at night to save on the cost of electricity. The reasons she gives are that it will be more economical to run because of this. As far as I am aware the cost of a new 13 Amp AGA will be very close to the running costs of an oil fired AGA. The only differences are with a 13 Amp AGA you are aren't going to have to service it twice a year like the Oil one. You won't be able to heat the water with the electric one as it doesn't have a boiler.
There are independent companies that also do conversions on Oil AGAs so that they either have an injection unit or an electric unit fitted so that the AGA works with a 13 Amp plug. See AGA cooker conversions. So it may be a cheaper consideration to have your oil AGA cooker converted to a cheaper way of running rather than replacing it in total.
To get it looking like new you can get it either cleaned professionally by a company such as ourselves and/or get bits or all of it re-enamelled by a company such as Hytech base in Weston Super Mare in Somerset: AGA Cooker Enamelling . To to get the AGA top done costs about £400 and to get the whole AGA enamelled would be about £1400. You would also have to get someone to dismantle the AGA so that you can send it off to be enamelled.Google+