Like someone mentioned, the sun is gonna be your biggest issue. Ive been really satisfied with the Portkeys PT6 5.2 Inch 4K HDMI Touchscreen Monitor lately. Its cheap, lightweight, and works well for LUTS.

• Pair it with a Zitay Ultra Thin Full HDMI to HDMI Cable
• Use a SmallRig Monitor Mount 2903B for the top handle Seriously, this setup is basically perfect for a $300 budget.

I was in the exact same spot when I first got my FX3 and that budget limit is totally doable tho. The built-in screen is okay for indoors but once you hit those bright beaches in Bali, you wont see a thing. Honestly I am very satisfied with how this cheap setup performs for the money. Heres what I recommend to stay under that $300 mark:

• The Feelworld F6 Plus 5.5 Inch 4K HDMI Touchscreen Monitor is a life saver. It is super lightweight which is huge for travel and the screen is plenty bright. No complaints about the build quality for the price.
• For the cable you need a full size HDMI to HDMI. I use the Kondor Blue Braided High Speed 4K HDMI to HDMI Cable 12 Inch and it works well since it doesnt dangle everywhere.
• You also need batteries for the screen. I just grabbed the Neewer NP-F550 2600mAh Li-ion Battery 2-Pack and they do the job just fine.
• To attach it to the camera I use the SmallRig Field Monitor Mount with Cold Shoe 2905. Basically you get a much bigger view for checking focus and you can even load your own LUTs to see the color. It is a game changer for vlogging and honestly way better than squinting at that tiny flip out screen. I am really happy with this combo and it saves you enough cash to actually enjoy your trip...

Been thinking about your setup since I saw your post earlier. In my experience shooting in tropical climates like Bali, I might actually disagree with the rush to get a budget monitor right away. Over the years, Ive found that many cheap panels wash out so badly in direct sunlight that they are basically useless anyway. I think I recall hearing some chatter in the forums about certain HDMI connections causing minor lag or signal drops on the FX3 when recording in high frame rates, but I am not entirely certain on the technical specifics there. If your budget is capped at $300, it might be safer to stick with the built-in screen for now and put that money toward extra batteries or even a high-quality ND filter. Not sure if that fits your plan, but its just something Ive learned after trying many different rigs.