It depends... Does he have enough money to go out with his friends but not enough money to buy you a birthday gift? In other words, do you believe him that he didn't have the money to buy you a gift?
Did he do anything special for you that does not involve spending money such as making you a card or writing you a love letter, etc.?
If he really didn't have the money to buy you anything don't let it bother you. But, if he didn't do anything to make you feel special on your birthday I think you may consider finding a more caring boyfriend.