Adam, if you put blades on a brick it would be better than the Razor IMO lmao. The HK450GT is a great helicopter with a proven track record. BUT, here lately I have really been looking into the Tarot 450 Pro V2 Super Combo. It comes with everything you need (less Tx/Rx) to get it in the air, and you have to put it together. Everything is there and it's less than $300. I almost purchased it the other day until I found another deal thats going to prove even more epic hehe.
But, if you are looking for the cheapest build possible, get the HK450GT from the USA warehouse, get 4 MG90S servos (I used one on the tail and it was decent, not perfect, decent), and the Detrum GY48V gyro. Servos and gyro from hobbypartz. If you want a little better tail, get the Servos only from hobbypartz, but cut the MG90S down to 3, adn get the EXI D213F digital servo for the tail. Or, get 4 of the EXI servos. But get the gyro from HK. It was named the Assan GY250, but they have branded it as HK now. Works great when I had it, but I had the Assan.
And yes, you can use everything from your 450 if you wish, servos and gyro included. They will fit.