I am not from China, therefore I cannot speak to how things work in your country... but I am grateful that here I could choose the instrument I want to play myself, and purchase it from where and whom I want. I do find it odd that any conservatory would demand that eligibility is based on the fact that you need to use one of the most expensive instruments available, irrespective of if you have accumulated the skills to take advantage of it or not.
I will make a few comments, though...
Concerning:
" I saw the difference between the original grille and the wooden grille. Need to buy more? Can I enjoy some customized services when I buy nova, such as size, button color, etc"
If you throw enough money at the manufacturer, they can pretty much do anything you wish. Musicians that have requested custom options like additional keys and such (for example a PA with 48 or 49 key right hand and other custom specifications ), are having them done, no problem.
Concerning:
"Excluding tax and shipping, what kind of price is suitable"
The only people that could give you that information is the manufacturer, or in your case, possibly the person you are possibly going to purchase from since they are the ones that are going to speak to Pigini with your specifications and order. You are talking one of the most expensive instruments around, so a very deep pocket is going to be mandatory, no matter what specification of a Nova you ultimately get. No one here works at Pigini, so that is not something that we can accurately tell you.
I wish you luck and success with your research and purchase.