Hi Marek,
this is possible with the new placeholders {$OffersMainPrice…}, e.g. {$OffersMainPriceFormattedPrice}.
It always keeps the main price only which is delivered by the Amazon API. Not the lowest new or used price. And if the main price is not set / empty, you can enter a text in the options which should be shown instead. The option label is „Empty main price text“.
Check the new placeholders at the end of the table on: http://www.wp-amazon-plugin.com/placeholders/