Story about a ship that changes size and a group of siblings

Question

I'm trying to identify the a children's fantasy book. My sense is that it's pretty old (before 1950) but I could be wrong.

At the beginning of the book, one of the boys in the group buys a little model ship. The first inkling he has that something funny is happening is that it changes size so it will fit in his pocket. Then in the rest of the book, I think it becomes life size and he and his brothers and sisters use it to travel places by magic.

One thing I specifically remember is that they they encounter someone who wants to take the ship away from them, but finds he can't. It turns out you can only acquire the ship by paying slightly more than all you have in the world. In the boy's case this was easy: he had gotten an advance on his allowance from the next week.

Answer 1

This is The Ship That Flew by Hilda Lewis. It was originally (self) published in 1939, but then re-published in 1958 in hardcover by Criterion Books

When Peter sees the model ship in the shop window, he wants it more than anything else on Earth. But this is no ordinary model. The ship takes Peter and the other children on magical flights, wherever they ask to go. Time after time the magic ship takes them on different exciting adventures, to different countries, and to different times.

This review mentions the cost of the item.

In a dark little shop, in a dark little street, Peter finds a little ship that costs him "all the money he has in the world - "and a bit over." This seems like a high price but it takes him into a magical world.