stock_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
<data>
    <record id="view_production_lot_form" model="ir.ui.view">
        <field name="name">view_production_lot_form</field>
        <field name="model">stock.production.lot</field>
        <field name="inherit_id" ref="stock.view_production_lot_form"></field>
        <field name="arch" type="xml">
            <field name="stock_available" position="after" version="7.0">
                <field name="cost_method"></field>
                <label string="Cost Price" for="standard_price" align="1.0" groups="base.group_user"/>
                <div groups="base.group_user">
                    <field name="standard_price" attrs="{'readonly':[('cost_method','=','average')]}" nolabel="1"/>
                    <button name="%(action_view_change_standard_price)d" string="update"
                        type="action" attrs="{'invisible':[('cost_method','&lt;&gt;','average')]}"
                        class="oe_link" groups="product.group_costing_method"/>
                </div>
            </field>
        </field>
    </record>
</data>
</openerp>