What about instead calculating 1000 per hp, calculate 5500 gold per hd? Constructs have d10 for hp which is about 5,5 hp/Hd. So your calculation wouln't change but we don't have to mess around with HP (Which is IMHO a bit better because roleplaying-wise a wizard can't think about precise HP if he's calculating his new golem, barely a rough guess of his toughness could be made. and this is IMHO better solved with HD then with HP itself).