[...snip...]
    <xsl:apply-templates select="product">
       <xsl:sort select="
                concat('0',price[@curr='USD']) +
                concat('0',price[@curr='GBP']) *1.47275  +
                concat('0',price[@curr='EU']) * 0.864379 "
             data-type="number" />
     </xsl:apply-templates>

[...snip...]
    <td align="right"><xsl:value-of select="
         format-number(
                concat('0',price[@curr='USD']) +
                concat('0',price[@curr='GBP']) *1.47275  +
                concat('0',price[@curr='EU']) * 0.864379 ,
    '#,##0.00')
"/></td>