that's vs it's

[cielo]

Hi everybody,
i'm a bit confused..could u help me?
i'm at the cimena, i have just bought two tickets..the ticket seller gives them to me and says 'that's £ 20'

i was wondering if it is possible to say ' it's £ 20' instead of that's

they're (the tickets are) £20

how much are those shoes? they're £40

how much is that dress? It's £ 30

thanks in advance

[Alan]

Not really.

"That's" here means specifically "You need to give me...(right now)": it is stating the total amount of payment required rather than simply responding to an enquiry about prices.