Per the U.S. Mint, a quarter has a nominal mass of 5.67 g. $500 = 2000 quarters. Doing the arithmetic, that comes to 11.34 kg or 25 lbs.
As correctly put by Nikilav Venkatesh, Joker never knew Batman's identity. And it really didn't mattered. Remember when Joker explains why the city needs a class of criminal. Criminals were scared of a mask and not of the face behind that mask.
Perry was diagnosed with a degenerative bone condition and a hip replacement was required, and as he was reluctant to rush into the surgery, Perry wanted to postpone the tour. The remaining members waited until 1998, nearly 17 months after Perry's injury, before making a decision on Journey's future.