New or old ds?

my friend is selling me a used nintendo ds and pokemon diamond and saphire for 50$, i don't really care about the saphire though, and the new ds lite at the store is 130$ and the game is 30$, so around 160$, but i have a gift card for 50$ and another best buy card for 30$ so it's like just 50$ for the ds but i have to buy the game for another 30 so which is better 80$ for a new or 50$ for a used...? also about what is the life expectancy for a ds? i know i already asked this, but i want more opinions