'ShowPriceRegularPrompt' is just a style, it's not going to display any text on its own. If you need to display that prompt in your customproductlist package, you need to do it like we do in our default packages. Get the prompt name:
Code:
<xsl:param name="pSalesPromptName" select="aspdnsf:GetMLValue(SalesPromptName)"></xsl:param>
...then pass that to GetVariantPrice:
Code:
<xsl:value-of select="aspdnsf:GetVariantPrice(VariantID, number(HidePriceUntilCart), Price, SalePrice, ExtendedPrice, Points, $pSalesPromptName, TaxClassID)" disable-output-escaping="yes" />