One thing that it could be is altitude. Air gets thicker and thinner as alt changes. I'm around 5k feet and my tail was underpowered so I had to adjust the mix. I wonder if you are closer to sea level than the factory and that's why yours had the problem. Also because the batts were toast, it maybe could have got some heat damage in a container or somewhere else along the line.

As far as it being expensive... yes it is, but pretty much so is every other decent heli out there. A few parts they really charge alot for, like the spindles (1 for $6 where a trex 450's are like 3 for 6). The trick is alot of the esky parts fit the blade and are alot cheaper. They just take longer to get here from Tiawan, but I am not sure about where you live. $25 for woodies is quite expensive. There's a site that has woodies for $8 bucks, and another one with plastic coated foam blades for $3.75. Anyways basically yeah it is expensive, but there are also deals to be found =)

good luck with your heli and I hope you get it back in the air