I'm assuming you're using attributes / options to select the price? If that's so, then in your product template (which I would recommend using - Contemplate is a fantastic module) you could just check and if the attribute exists for that product, instead of showing THE price, show the text "Prices from.." and the first option, or whichever option is associated with the lowest price.

If you only want to do it for some products, and not all, maybe making a new Checkbox (utilizing CCK) to be a Boolean Yes/No (True/False) - along the lines of "Instead of showing the price, show the lowest price?" and if it's checked, again in your template, check for that value to exist. And if it does, then proceed to show the starting price.

Something like that anyways, would be my recommendation - spitballing, as usual