Not that I think that 45 is to much and not that I cannot buy a new slot for gold-gems, but
I am always upset about pricing that does not respect that I already bought the base game for 50.
So here a proposal for a symbolic gesture:
If you buy it and use it stand alone you get HoT and base game with 5 slots,
If you buy it and attach it to an existing account you get HoT and 1-5 slots at your existing account.
Ceterum censeo SFR esse delendam!