"Very" is normal statement "Too" shows impossibility or negativity. in your example, it is VERY expensive but you can buy it. However, it is TOO expensive that means you can't buy it or imposible to do so.

Yes, they are different. 'Too' is negative. If something is 'very expensive' this means that it costs a lot. But if you say that something is 'too expensive' this means that you don't think it is worth the price, or that you haven't got enough money for it. You don't want to buy something that is too expensive. If your husband buys you a necklace that is very expensive, you might be happy. But if he buys you a necklace that is too expensive, you'll be angry with him for wasting money.

Yes, a slight difference. If you go to buy a watch, and it is too expensive, then you are saying you will not buy it, because you do not have the money, you could buy that watch for less elsewhere, etc. If the watch is very expensive, you are saying that you don't like the price, but you are not saying that you will not buy it. You might still buy it, even though you don't like the price.