eiru_salon_spa/models/project_service_material.py

# -*- coding: utf-8 -*-
from openerp import fields, models, api

class ProjectServiceMaterial(models.Model):
    _name = 'project.service.material'

    product_id = fields.Many2one('product.product', string='Productos', domain=[('sale_ok','=',True)])
    task_id = fields.Many2one('project.service.task',string="Trabajo")
    amount = fields.Integer(string='Cantidad', default=1)
    price = fields.Float(string='Precio Unitario')
    
    @api.onchange('product_id')
    def get_price(self):
        self.price = self.product_id.lst_price