Im no super do-it-yourselfer but I installed a new water heater and it was fairly easy. Home depot, a station wagon, a hand truck and some basic tools and its done. Cheaper than repairing my old gas unit. There was a little dicking around with sweating in the pipes but nothing that bad. I think it cost me 400-500 bucks for a new unit, a new hand truck, some parts and $50 for the trash removal for the old unit.
Paying 900 for a repair sounds like a rip off but that is the nature of appliances. They usually cost a lot less just to replace.
I have saved thousands going to a web site for appliance repair
http://appliantology.org/forum/23-water-heaters/ I have never had to call a repair person since I found the site.