Which RX100 model do you have exactly? The sizing changed a bit on the newer ones so I wanna be sure! If you need to stay under $30, check these out:

• Kiwiotos Anti-Slip Adhesive Camera Grip for Sony RX100 IV V VI VII
• This thing is fantastic and stays on way better than the generic ones!
• UURig R017 Camera Baseplate for Sony RX100 VII M1-M7
• It is a solid metal base that adds a tiny bit of bulk for much better handling. Both are awesome for travel!

Just saw this thread and wanted to jump in. Regarding what #1 said about these cameras being like bars of soap... it is honestly a nightmare. I tried some of those generic adhesive rubber pads last year and they just peeled off in the heat, total waste of money. Since you are on a tight budget and need it fast, look at the JJC HG-RX100 Metal Hand Grip Extension. It gives your pinky a place to rest and has a cutout so you can still swap the battery without taking the whole thing off. Unfortunately, a lot of the cheaper options have issues:

• Plastic grips often crack near the screw hole if you overtighten them.
• Many generic baseplates block the flash or the screen hinge on certain RX100 models.
• Avoid the MegaGear MG1452 Ever Ready Leather Case if you want a slim profile, it is way too bulky for a pocket. The JJC is probably the most reliable under 30 bucks, even if the finish isnt as nice as high-end gear.

Honestly, these cameras are like bars of soap. I have used a few different setups over the years and unfortunately, most of the cheap extensions just dont feel right or they end up blocking the battery door.

• Sony AG-R2 Attachment Grip: This is the official one everyone buys. It is basically just a piece of rubber with 3M tape on the back. I had issues with mine peeling off after a humid summer, which was way more annoying than I expected for something directly from Sony. It adds a decent finger hold but feels a bit flimsy for the price.
• SmallRig L-Shape Grip for Sony RX100 Series 2230: I tried this for a bit. It is much more secure since it screws into the tripod mount, but it makes the camera feel way heavier and less pocketable than the marketing suggests. It is not as sleek as I hoped it would be, tho it definitely wont fall off like the sticky ones. I would stay away from those random off-brand stick-ons you see for ten bucks. The adhesive is usually garbage and leaves a nasty residue. If you are leaving Tuesday, just get the official Sony one and make sure you clean the camera body with some rubbing alcohol first. It is not the perfect solution but it is probably your best bet to avoid a disaster in Tokyo. Just dont expect it to feel like a pro DSLR grip or anything.