purchase_order_update_prices/views/view.xml

<?xml version="1.0"?>
<openerp>
<data>

          <!-- Add update product cost price option in purchase order line. -->
    <record id="view_purchase_update_product_cost_price" model="ir.ui.view">
        <field name="name">view.purchase.product.prices</field>
        <field name="model">purchase.order</field>
        <field name="inherit_id" ref="purchase.purchase_order_form"/>
        <field name="arch" type="xml">
            <xpath expr="//tree/field[@name='state']" position="after">
                <field name="update_cost_price"/>
            </xpath>
        </field>
    </record>


</data>
</openerp>