Forum:Ultimate offering confusion

I was wondering if the 500 life points is a cost of activation, or the cost of each extra summon/set. So for example, let's say I activate ultimate offering on my opponents battle phase and I summon a monster. Do I pay 500 for the activation of Ultimate offering, then pay another 500 for the monster, or just 500 for the activation and the monster is summoned due to that 500 life point cost?

Another question is can my opponent use my ultimate offering to summon more than once, or is it just for me?

Last question is can I use ultimate offering to summon more than 1 extra summon/set, or does it just allow me one extra summon/set. The new text says "You can pay 500 Life Points to Normal Summon or Set 1 extra monster", but it does not say if I can use it more than once per main phase or turn.

Thanks in advance.