Generate Elliptic Curve Private Key from User Passphrase?
Using PBKDF2/Bcrypt/Scrypt might be the least-bad way, but that doesn't mean it's a good way.  If your passphrase is puppies, it doesn't matter whether you use PBKDF2, Bcrypt, or Scrypt: you've got serious problems.  If someone tries to crack your key, you're going to be toast: your key will be cracked within minutes.

Bottom line: this sounds like a bad idea to me, if there's any possibility at all that the passphrase might be weak (which, in practice, there will be).
I would not use this to protect my money.

Instead, you should be generating a truly random or cryptographically-strong random number for the private key, then storing the private key somewhere safe.  If you want to store the private key in encrypted form, you can derive a symmetric encryption key $K$ from a passphrase and store the private key encrypted under $K$ (though please understand that this will likely be vulnerable if someone manages to steal a copy of the encrypted private key).