Hello and welcome Hellie,

As there are loads of training schools about it is a minefield. I managed to get my better halfs CBT for £49 via Groupon, so that might be worth a look.
She took it with the guys at Mega Motorcycle Store and then decided to take her full test.
My advice would be to do your CBT and see if you enjoy it that much that you want that bit more power, you could always stick to the 125 licence if that is what you feel comfortable on.
If you get on with it like a house on fire then bite the bullet and take the big test, loads of bikes out there for 125 money at the moment and there are plenty of members out there who are more than handy around their bikes.

If you find anything nearer Carterton give me a shout and I will happily come and check it over, test ride it and tell you whether it is worth buying.