Fifty dollars sounds rather a lot - you can buy a decent light for that money. But, that's what you pay when you're buying 'genuine' parts. I have a little SureFire diffuser on one of my JetBeams, just a rubber sleeve with plastic insert, and it cost a third what I paid for the entire light!
However, unless I'm mistaken, you can use any number of third-party alternatives. Apart from being much cheaper, they'll also let you go for something much brighter (with reduced run time) if you want to.
This stickied forum thread on CPF looks promising - it's a list of P60 drop-in modules:
http://www.candlep...hread.php?t=217252