A good pair of batting pads is one of the best investments you can make. They can last you a good few seasons if you don't rag them around too much.
As with most protective gear the higher end tends to offer more protection at a lighter weight and is more flexible and batting pads are no exception.
The pads in the $50-$60 range are good quality and suitable for most league cricketers. Those that come in at around $80-$100 are for the guys who face a hard ball and are used to batting for long periods.
The top of the range, $100 and up are the same pads that the international boys use when they are doing their thing.