Best would be to have ticket combined for both Madame Tussads and Repley's believe it or not and it would be around 50$ per adult.
If you live in NY, NJ or Connecticut you get a discount with valid ID. If you buy online you save up to $5 per person. You should really check your options directly on the website. Child age may affect prices. Ticket type affect prices ie silver is $10 cheaper than gold. Gold gives you a bit extra. Then there's platinum price. Go to the website and chose options that suits your needs... Link is below. https://www.madametussauds.com/new-york/en/tickets/
You should check Groupon they always have deals for Madame Tussauds.
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I believe if I remember correctly there's 2 different price range one in the thirties that's without the additional shows and another 1 in the fifties and that's with the shows and I would definitely recommend to do the shows and I had no children with me so I do not know the child surprised if it varied
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