If they have parts for the trex 250 they should parts for the 450. The 450 is probably the single most popular CP heli in the world and should be easy to find the parts for. The parts will be interchangeable on most clones.

People worry about the crash cost of Align because the kits are more but I really don't see much difference in the cost of the common crash parts. In fact, I think the Align shafts work out cheaper since you can buy them in packs. My blade CP shafts always came individually for around the same price as a trex 450 2-pack of main shafts or 3 pack of feathering shafts. Woody main blades were about the same also, maybe $2 difference. The only crash that has really cost me was when I broke a motor wire and had to replace the motor. As long as the electronics are intact it's generally not too bad IMO. Though my budget isn't quite as tight as some peoples so....

I don't have a blade 400 but I've seen a lot of people recommend upgrading the servos right off the bat, so keep that in mind. I've flown a blade 400 and honestly feel a trex 450 or clone with decent electronics is superior, more stable and easier to fly.