Jetson only wants twenty bucks for a new charger. If anything you want to spend more and get some assured quality, which a cheap-ass Far East charger is never going to provide, which is possibly why you need another one already.
It looks like they use a simple pin plug, although its not possible for me to tell what the size is from the web site. But seeing that little pin I can say its no more than a 2a charger most likely.
Its a 48v 7.5ah battery that supposedly takes up to 5 hours to charge that tiny battery, so I take that back, its probably a 1a charger. Which tracks with use of such a small pin on the end of the plug.
Best bet is buy a replacement from Jetson. If you are looking for cheaper, you may as well just light a match to the bike now and get it over with.