Been crunching some numbers on this because those 61MP RAW files are huge. You're looking at like 120MB per uncompressed file, so at 10fps, you're hitting the bus really hard. If you want the best value under 300 bucks, you should check out the ProGrade Digital SDXC UHS-II V90 128GB cards. They often come in a two-pack that fits your budget perfectly. Sustained write speed is around 250MB/s, which is basically the limit for SD tech. Unlike V60 cards, these wont drop below 90MB/s which is key for clearing that buffer light. Another solid path is the SanDisk Extreme PRO SDXC UHS-II 128GB V90. SanDisk is basically the standard for reliability, though you pay a bit of a premium for the branding sometimes. It hits similar 300MB/s read and 260MB/s write peaks. If you go this route, you’ll definitely notice the buffer clearing way faster than those old cards you've got now. Just a heads up tho, even with V90 SD cards, that sensor will still fill the buffer if you're holding the shutter down for long stretches. If you can find a deal, the Sony CFexpress Type A 160GB TOUGH is the only way to truly unlock the camera, but it's pricey. For Costa Rica, I’d probably just grab the ProGrade V90 dual pack. It’s a good balance of speed and capacity. Just make sure you're shooting in Compressed RAW or Lossless Compressed to give the buffer a fighting chance. It makes a world of difference for birding.

Honestly those old cards are gonna choke on those 61MP files every single time. Ive been there and it totally sucks when you miss a shot because of hardware limits. You basically have two paths with that 300 dollar budget but you gotta be careful because the a7R V is a massive data hog. If you want two cards to stay within budget, I would suggest looking at Kingston Canvas React Plus 128GB UHS-II V90 SD. They are usually way cheaper than the Sony branded ones but perform almost as well for clearing the buffer. I use them for birding too and they clear much faster than generic cards. Just make sure you get the V90 rating specifically or youll be stuck watching that red light blink forever. Now, if you want the absolute fastest clear time possible, you might want to consider getting at least one Lexar Professional CFexpress Type A Card Gold Series 160GB. It might push your budget if you buy two, but the speed difference between SD and CFexpress Type A is huge on this body. Be careful though, make sure you have a reader that supports them too. Also, stick to reputable retailers because fake cards are everywhere online and they wont hit the advertised speeds. Just my experience based on losing shots before... definitely dont risk it with slow cards on a big trip like that.