You're a new player, aren't you?
Yes, the prices to upgrade the girls are high. That is intentional so that players don't start to gather money and sit on hundreds of millions like it was the case before last summer big update.
Yet, the current situation, despite some tweaks, is still difficult, and a significant tweak in this regard is planned before the end of the month (see late informations about harem 2.0 and stuffs like that)