A product with fixed quantity

I want a product that can only be purchased per 500, 1000 or 1500 pieces. So not for example 450 or 1205 pieces
The price per piece is for example:
For 500 pieces: 1,75 per piece
For 1000 pieces: 1,25 per peice

I've created an attribute with amount of pieces: 500, 1000 or 1500 and specified a total price:
For 500 = 875 euro
For 1000 = 1250 euro

This means that the price will be dispalyed as 875 or 1250.
Can I do this in a different way so that the price of 1,75 or 1,25 is displayed (lower value to be displayed to customer)

see http://www.flexiflow.be/index.php/detai ... kesen.html
thanx