You have to return a value in that if statement. If you do that, the rest of the code won't be executed.
Code:
if(!is_user_alive(id))
{
client_print(id, print_chat, "You can't buy an antidote while you are dead!");
return PLUGIN_HANDLED;
}
Biohazard uses fakemeta to retreive & set a player's amount of money. Cstrike is faster than fm, so your method is fine.
__________________