Maybe It's the Nerd In Me...

...But on the Big Bang Theory, how does Penny have an apartment in the same building as Sheldon and Leonard, who share an apartment? Granted hers is way smaller, but a waitress barely making ends meet versus two scientists with doctorates working at a university? Stranger things in life happen and I guess it is a pretty crappy apartment building(the elevator has never worked) which would let the two of them save money for stuff they like....