But especially if you buy a book for $15 or so, the difference is so minimal. And having the book gives you the other coupons...my western WA book has a coupon for Super Shuttle, which saved me $4 off on my transportation to DLR in December and January. If you're doing other parks, there are coupons for Universal (though I'm not 100% sure it's on the CA Universal, b/c all I'm remembering is it stating Orlando).
But if you don't need those, then yeah, borrowing or even buying a card would work (and, lol, you can shop on ebay through sunshine as well and get 1% back....).