eiru_product_extra_price/templates.xml

<openerp>
    <data>
        <record id="product_template_form_view" model="ir.ui.view">
            <field name="model">product.template</field>
            <field name="inherit_id" ref="product.product_template_form_view"/>
            <field name="priority" eval="100"/>
            <field name="arch" type="xml">
                <xpath expr="//page[@string='Sales']/group[@name='sale']" position="before">
                    <group>
                        <field name="list_price" string="Precio público"/>
                        <field name="minimum_price" string="Precio mínimo"/>
                        <field name="maximum_price" string="Precio máximo"/>
                    </group>
                </xpath>
            </field>
        </record>
    </data>
</openerp>