Yes, with current handset contracts, any early termination with no proper reason will incur 1-to-1 cost for the main subscription and the VASes that's still on contract.
If you're on any discounts, the discounts will NOT apply and you've to pay the full price too.
So like what
@Kiwi8 said, you're better off staying in your current contract and port out after it ended.
Plus, if you really really want to port to Giga with whatever promo right now (afaik most promos now basically is the rehash of the previous promos), you can always sign up Giga separately and port in after your SingTel contract ends.
There's no port in only promotion it seems, unless my source is wrong?