Nursery fees struggling to get head around!

My daughter will be three in autumn.
I want to send her to nursery/playgroup for her 15 hours funded.
She hasnt been before as im at home.
I found a fab nursery with a great reputation but im struggling to understand the fee system.
As i will only be sending her term time they have talked about retainer fees/ top up fees but im worried im not going to be able to afford it.
They havent said how much as i wont know until later, when and what days she can go.
I feel silly not being able to get my around it and i cant ask friends for advice as those with kids all work full time anyway.
I feel like an idiot!
Anyone else pay a retainer fee for term tiime only and how much is it?

 

Thanks for your reply, can you remember roughly what you paid ecah day? Xx