Happiness is undoubtedly a state of mind. It is completely a personal choice of peoples, whether they want to be happy or not. It is nothing to do with their financial conditions - they could be rich or pauper. However, the level of happiness can be enhanced by good health and healthy bank balance.
Just imagine, you are living on paycheck to paycheck basis and somehow for a month it got delayed due to any unforeseen circumstances. Will your happiness not get affected if you have to pay room rent and purchase other basic things for living? No doubt, if you haven't planned for these circumstances in advance, it will definitely create tension and deplete the level of happiness, however little it may be. Even sometimes, it becomes demoralizing due to shortage of money.
It is true that the fountain of happiness is inside you and to search it outside is futile. In other words, if you are not feeling happy internally, you cannot find happiness outside. Definitely, the outside world plays their part to enhance your happiness if you are already happy internally. Money is also one of the means, which can enhance your happiness by improving living standards: quality food, better medical facility, going to the movie and holidays in the hills or buy the sea. Most importantly, a healthy bank balance provides you the resources and time to invest on realizing your higher purpose else; it can be lost in only making both ends meet.
Finally, you do not need to have million in your account and waste your entire life in making money only, but the bank balance should be enough to provide you comfort, recreation, resources and time. Most of the people do have the regret in the end of their lives for not doing whatever they wanted to do due to lack of resources and time. Therefore, try to create wealth sufficient enough for you to fulfill your desire and do not have a regret in later part of life.