How much to spend on 'thank you' gift for nursery teacher?

[JinxyCat]

I've been useless and haven't managed to organise a gift for my son's nursery teacher - so my only option is vouchers.

I'm considering Amazon vouchers, how much is reasonable to give?

I'm in London, it's a state school, and he attends 2 1/2 days a week. We really like his teacher, and I don't want to over/under spend.

Also - should I be doing a gift for the teaching attendant?

I get the kids to make them a home made card each which seems to go down well

Thanks @Nevercan - we made cars last night and I got them Amazon vouchers which hopefully they'll like!