When I bought my first car I had the same joy as when I got my first bicycle, or even when I completed my education or got married. It means that joy is not determined by the value of money or time spent on something that rewarded you. It also means, and perhaps we don't realise, that it fades away in a while.
Joy is an emotion, and hence it has to be temporary. And, we, in our day to day language, tend to misunderstand joy with happiness. That messes up everything.
On the contrary, happiness is not an emotion, it is a state of mind. It is a state of being conscious, composed, contended and complete. I can be happy whenever we want to, needless to say even perpetually - only and only by my own choice.
Would you equate happiness with contentment? If yes, do you think it hampers progress?