The way to display the products price need to be very extensible, to fill most of needs.

What about the idea to tokenize the display of the products by providing some tokens :

[sell-price] = display the normal sell price
[sell-price-tax] = display the sell price with a tax included.
[global-currency] = the currency set up in the shop
[local-currency] an eventual local currency set up in the "my accoun" page, in case of some multicurrencies features.

With an admin option that provide a textarea in which you can put the text you want + token like that

maybe you could provide too this same textarea in product page, in case of, for some products, you want to override the global setting.