MSRP price showing for each Product attribute

Hi All,
Can anyone help me with a problem I have for my site.

I have products with attributes and each attribute has a MSRP price. However in Zen cart it always shows the MSRP price of the product added.

For example
Product is Barley seeds which sell in various sizes (0.5kg, 1kg and 5Kg) the prices are as below

I add a product starting with the 0.5kg product MSRP = £2 and Price = £1.

Now I add the Attributes name = Weight
Options 0.5kg (default), 1kg, 5kg

I add the prices for each of the attributes. I don't know where else I can add the MSRP for the attributes.

Everything is fine on the products page and the MSRP, Our Price, You Save, with default options attributes showing.

However when I choose the option 1Kg or 5Kg then MSRP remains the same (£2), our price shows correctly, You Save is incorrect.

Is there a way I can have the MSRP show for each of the options?

Many thanks for any help given.

Vinny