Sarah has anywhere from 0 to 99 cents, Jane has 9 dollars more, and the book costs at least 9.01 dollars + twice what Sarah has.
If the book has a cost of 'x', Sarah has 's' dollars and Jane has 'j' dollars, the following equations true:
x = s + 10 (1)
x = j + 1 (2)
There's also an inequity we know of:
s + j < x (3)
From (1) and (2) we find that j = s + 9
Substitute in (3) to find:
2s +9 < x (4)
Then from (2) we know x = s+10, so substitute in (4):
2s + 9 < s+10 (5)
We know s cannot be negative, so we are certain boh sides are positive. If we deduct (s+9) from both sides of (5) we get the following inequity:
s < 1
As pointed out in comments, 'no change' is deemed to imply 'no coins, only bills'. Given there is no bills smaller then 1 dollar, and the monetary amount cannot be negative, by definition s has to be 0.
Therefor Sarah has 0 dollars, Jane has 9 dollars and the book costs 10 dollars.
Details on the non-integer solution:
0.99 dollars, 9.99 dollars and a 10.99 dollar book works (and any smaller amount for s).
If Sarah has ONE dollar, and Jane has 10 dollars, they'd both be able to combine their money for an 11 dollar book.