RRP and sales price with VAT calculations

[OpenGlobal]

I have a customer who wants to enter two prices in the backend, the RRP and the final sales price that the customer pays (these will both be inclusive of VAT). But they want to display the ex-VAT price as well as the RRP and sales price.

eg.

Backend:
RRP: £499
Sales Price: £449

Frontend:
RRP: £499.00
Sales price: £449.00
Saving: £50
Sales price (ex-VAT): £374.17

I'm going around in circles trying to get this working to (a) display those prices and (b) charge the correct price at the checkout (£449 in the example above)

Can this be done? If so, how? Or am I just going to have to put the RRP in a custom field instead?

OpenGlobal