A change in my savings goals

An opportunity to visit a part of the United States I have not see before has arisen. My dad's mother's side of the family whose German relatives hosted the family reunion in Germany in 2007 is now looking to gather in Missouri in September 2010. While I have not committed myself to the trip, I am interested enough that I started looking at where I could save money for this trip. My reasoning is twofold:

1. Saving money for this trip means it does not come out of my emergency funding nor steals from my other financial goals.


2. If I decide against the trip, the money can be redistributed or used for other purposes.

The drawback to my savings plans: I have no idea how much I need for the trip. My mother suggested I aim for $500. Starting with that number, I carefully analyzed my spending plan and my current savings amounts. This is what I have decided:
$10 from my monthly cat care allocation (I have only one cat to care for)
$10 from my personal care allocation (my spending has decreased in this category)
$1 from my gift spending account (buying secondhand and making items has given me more breathing room here)
$10 from savings (I reduce the amount to savings by this amount every month)
$10 from house savings (I decrease my contributions by this amount each month)
$41 total

Since there are 13 months between now and September 2010, I estimate that I can save $533. That does not include money from extra checks (there are three between now and then) or any other sources. This is a good start for my vacation fund and an extra cushion if something else arises. I may change my mind after I see the estimated price tag for the family reunion but more savings will help fund my other financial goals.

What do you think of my changed plans?