I totally get the frustration! I had the same issue at my cousins graduation and it was a nightmare until I looked at the actual bitrates. You honestly dont need pricey V90 cards for most A7IV modes. I saved tons of cash using these:

• Lexar Professional 1667x 128GB SDXC UHS-II V60
• ProGrade Digital SDXC UHS-II V60 Gold 128GB They handle 4K 10-bit like a total champ for way under 100 bucks! Amazing performance for the price!

Jumping in because I am obsessed with the A7IV! It is seriously such a powerhouse for weddings and you are gonna have a blast using it! Honestly, the V60 vs V90 thing is a total headache at first but you can definitely get what you need under a hundred bucks. For weddings, I always tell people to look at the Kingston Canvas React Plus 128GB SDXC UHS-II V90. It is an absolute beast and surprisingly cheap for a V90 card. It handles every single video mode the A7IV has without breaking a sweat, so no more of those annoying error messages mid-vow! If you want to save even more and maybe grab two cards for redundancy, check out the Sony SF-E Series 128GB UHS-II V60. They are fantastic and since they are Sony branded, the compatibility is just flawless. I love these for long ceremonies because they run cool and I have never had one fail on me yet! Just a quick tip for the big day... always format your cards inside the camera menu, not on your PC or Mac. It keeps the file structure clean and prevents those random card error popups that ruin shots. Also, maybe grab a spare battery because 4K recording is a total power hog! You are gonna kill it at the wedding, just breathe and let the autofocus do the heavy lifting... it is magic on that camera! Let me know if you run into any other weird settings issues before the big day.

Saw this a few hours ago and meant to jump in because I am dealing with the same exact headache right now. It is so annoying that a camera this expensive doesnt just come with what it needs to actually work. I have been getting those same errors on my older cards and it is honestly so disappointing... Since I am also trying to keep it under 100 bucks, I have been looking at a few but I am just as stuck as you are:

• SanDisk Extreme Pro SDXC UHS-II V60 128GB: Super reliable brand name usually, but honestly it is kinda pricey for what you get.
• Sony SF-M Series Tough V60 128GB: Everyone says these are great because they are tough, but they are almost always right at the top of the budget and feel overpriced.
• Sabrent Rocket V60 SDXC UHS-II 128GB: These are way cheaper which I love, but I am nervous because I dont know the brand as well. I still havent decided what to get because I dont want to ruin a shoot either. It is such a gamble when you are starting out.