How can we price our unreal engine arch viz projects ???

The simple answer is what ever the market will allow. Unfortunately RT is going to go the way of still renderings as more people learn to make them. The only thing you can do is educate your client and not sell yourself cheap as it hurts the entire industry. If they can’t afford it then don’t do it, offer them stills instead. I know most won’t do that because they need to eat.