I think I misunderstood your question.
It's the same cost to freeze wether you have 1 embryo or 10.
So I guess you have to weigh up wether you would be happy to freeze 2/3 embies (if that's all that's left over after transfer) or if you'd prefer to keep doing fresh.
The costs were slightly lower when we were going through all this previously.. and tbh, we never really thought it through properly. That said, if do the same again.. I couldn't bin 5 good quality embryos.