40. Some airline companies prefer to spend extra money on leather seats for their aircraft, sometimes twice as expensive as the others, because they last two times as long.
(A) Some airline companies prefer to spend extra money on leather seats for their aircraft, sometimes twice as expensive as the others, because they last two times as long.
(B) Some airline companies prefer to spend extra money, sometimes twice as expensive as the others, on leather seats for their aircraft because they last twice as long.
(C) Some airline companies prefer to spend extra money on leather seats, sometimes twice as expensive as the others, on leather seats for their aircraft, being twice as long lasting.
(D) Leather seats lasting twice as long as the others, some airline companies prefer spending two times the extra money on them.
(E) Some airline companies prefer to spend extra money on leather seats, sometimes twice as expensive as the others, for their aircraft because they last twice as long.

Source: Kaplan GMAT 800 edition 2008-2009 (pls help transfer to General Questions forum)

Explanation from the book:
40. The fact that everything is underlined in this sentence means that you have a lot of issues to consider. Start with something concrete. You know that sometimes twice as expensive as the others modifies leather seats so make sure that the two are placed next to each other in the sentence. Eliminate (A) and (B). Next, because they last twice as long is better and clearer than being twice as long lasting. Eliminate (C). Finally, two times the extra money in (D) makes no sense, or at least it distorts the meaning of the original sentence, suggesting that companies are spending twice the increase in cost rather than twice the cost of the other seats. (E) remains.

MY QUESTION:
E seems wrong to me, since 'their' refers to companies' while 'they' should refer to seats. This is pronoun ambuiguity. Why is E correct? thanks.

sometimes as expensive as others is modifier and should modify the seat belts so place near to seat belts,
E is correct.

Stacey,
Why is 'they' in the sentence not considered ambiguous?

Yes their is ambiguity w.r.t. "they" but this ambiguity is with every option and we need to choose least incorrect. So check for other things,like in this case, modifier "sometimes twice as expensive as the others" is used to modify leather seats,money,aircraft. In correct version it should modify leather seats. So C and E remains, "leather seats" is repeated twice and is redundant. So E is correct.