fixed price

I purchased the Multi Currency plugin to use in my travel agency, Some of the products, have the native price in US dolars, and some of them (the national ones here in Brazil) have the native price in brazilian reais. When I select ENABLE the Fixed price, it says that its going to overwrite the calculated price. I go to the product, it appears for me the price field in the 4 currencies I registered (reais that is the website currency, dolars, euros and rands). I Insert the price on the US dolrs field, but it doesn’t appers in the booking page. How I’m supposed to do that to use some of produts with US dolar native price, then converting to reais for the customer and some products registered in native urrency reais.