Dude, I totally feel your pain with those Canon prices! 350 bucks is basically a robbery when you just want a better grip. I picked up a third-party one for my R6 last year and it has been absolutely fantastic for my wedding gigs. You should seriously look at the Neewer BG-R10 Replacement Battery Grip for Canon EOS R5 R6 R6 Mark II. It is way under your 100 dollar budget and the build quality is actually super impressive!

• The dual battery slot means you wont be fumbling with doors in the middle of a ceremony.
• Buttons like the shutter and AF-ON feel really crisp and natural.
• It adds that extra vertical surface area so your hand wont cramp up during those 10-hour days. Its honestly such a game changer for the ergonomics. Just make sure the pins are clean before you mount it and youre good to go. Youre gonna love how much easier it makes shooting vertical portraits! Let me know if you need help with anything else before your Seattle trip.

^ This. Also, I went down a rabbit hole comparing the circuit boards on these third-party grips last year because I was paranoid about power surges. Most use almost identical pin layouts to the OEM version. I ended up testing a few for an R5/R6 setup and found some decent results under that 100 dollar mark.

• JJC BG-R10 Battery Grip for Canon EOS R5 R6 R6II usually runs about 85 bucks. It fits tight, though the texture isnt a 100% match for the Canon body.
• Meike MK-R5 MK-R6 Battery Grip with 2.4G Remote Control is usually around 90. The remote is actually super useful for long exposures if you do any landscape stuff on the side. The Meike grip felt a bit more substantial in the hand for me. Just watch your battery choice... the high-speed continuous shooting requires the newer LP-E6NH cells. If the grip doesnt communicate properly with those specific batteries, it might drop your frame rate regardless of the brand. I had that happen once mid-shoot and it was super annoying.

^ This. Also, avoid the super cheap stuff for weddings. Over the years, the Vello BG-C18 Battery Grip for Canon R6 proved much more reliable.

• Better seals
• Wont fail