In my experience tracking camera gear and high-end tech over the years, the standard apps like Camel just do not cut it for time-sensitive warehouse deals. If you want instant alerts, I recommend using HotStock. I have used it for several hard-to-find lens releases and the push notifications are practically real-time. They have a premium tier for about four bucks a month that increases the ping frequency, which is exactly what you need when you are competing for a single warehouse deal. Another option if you want to stick with Keepas data but hate their app is setting up Keepa to send alerts via Telegram. Keepa allows you to link a Telegram bot for notifications. It completely bypasses their clunky mobile UI and sends a direct push message to your phone the second their system detects a price drop. I set this up last year for my Sony GM body and it worked flawlessly, beating the email alerts by at least twenty minutes. Go with HotStock premium for the easiest setup, or link Keepa to Telegram if you want the absolute most accurate pricing data without dealing with their messy interface. Both will easily fit under your ten dollar budget and get you that lens before your Japan trip.

I had a similar headache last year trying to grab a telephoto lens before a trip to Iceland. Warehouse deals are brutal because they literally have like one item in stock, so if you are not checking the second it drops, it is gone. My current setup is a bit of a hybrid because I learned the hard way that relying on just one app is a recipe for disappointment. A few things I learned during that hunt:

• Warehouse grading is super inconsistent. Make sure to check the description because Acceptable sometimes looks brand new, but Like New can occasionally have missing caps.
• Set your target price slightly higher than your actual budget. Sometimes a seller drops it to $1820 and you miss it because your alert was strictly set at $1800.
• Beware of third-party scam sellers hijacking the buy box when prices drop. Always verify it says Sold by Amazon Warehouse before hitting buy. For the actual tracking, since you carry a work phone, you might want to consider keeping a tab open on your computer too. I actually started using PriceDropCatch on my work laptop because it pushes desktop alerts the second a price fluctuates. Between that and a basic scraper, I finally snagged my lens for about $300 off retail. Just be ready to check out with 1-click ordering enabled, otherwise someone else will grab it while you are typing your CVV code. Good luck with the Japan trip, that lens is going to be killer over there!