Yes, some of the suppliers have already priced for an on grid hybrid inverter, and some say that will cost more than their quoted on grid inverter, but still the inverter supply price difference shouldn't be more than THB10-20k surely.
Unfortunately I don't have the electrical knowledge to DIY, and I don't trust employing an electrician to install only. I've read about people ending up with systems that don't work. At least with a reputable supplier you have a chance to get it right first time.