I stayed at the Westin 2 years ago but arrive via plane, so didn't pay too much attention to the parking situation. However, a quick google search it appears that rates can be had for about $8-$12/day... but then it becomes a question of how easy it is to get to from the Westin. Worst case scenario would you have to take the shuttle from the Westin to the airport, then the airport parking shuttle to the lot you choose... it would be worth a few dollars extra, imo, to get something that was near the Westin (or whatever hotel it is that you receive)
I will add that for my own stay at the Westin, i arrived late at nite and then rented a car the following morning. I thought i would need to shuttle from Westin to the airport, then shuttle from airport to the car rental location... but when the shuttle driver asked me which airline i needed for departure and i explained any of them because i was actually going to catch a shuttle to the car rental place, he dropped me off en-route and i walked a block to the rental location... so always a chance that the shuttle driver will be as accommodating if the location you choose to park your car is along the hotel shuttle route.
Please remember to return to BetterBidding and use the PRICELINE and HOTWIRE links on the board to begin your travel purchases... or thru our sister site MAPSandHOTELS.com for your regular rate purchases.
Let us know your thoughts and how you'd like to proceed and we'll take it from there.