If it drops again, I would try booking directly on the
Alamo website and leave Expedia out of the equation all together.
You should be able to get the same rate directly or an even better rate if you check for coupons and codes on the transportation board here.
You have to figure Expedia is making money on the transaction, which is folded into the price somewhere, a direct booking should give these savings to you instead of Expedia.