Just to throw in my 2 cents - or tuppence if you prefer..
There's SOOOOOO many ways/tools to transfer files between a modern-internet-connected computer and a classic Mac. I'm by no means an expert, but because I was really bored during the pandemic, I've purchased and tried most of them. Allow me to share a little run-down:
FloppyEMU: expensive and slow, has some quirks about how to use it, but overall a very useful piece of kit. I don't know if you'd have to pay extra for import to the UK, but that would only make it even more expensive. It is especially useful if you want to use it on several classic Macs and even an Apple II if you want. If I were doing it all over again, I wouldn't bother buying the FloppyEMU.
SCSI2SD: v5 is much cheaper than v6, and you won't get any additional speed out of v6 with a Mac SE. So don't bother getting v6 unless you plan to use it with other devices too. But, there are better and easier tools than this. I found the setup of the SCSI2SD and all the hoops you have to jump through to get files on it to be annoying and fiddly compared to the other solutions - especially when you want to make changes to the drive images later, or add files later.
MacSD: more expensive than SCSI2SD, but it is VERY easy to use with a Windows PC, and it offers one killer feature: mounting ISO images of CDs in a round-robin fashion. You eject the CD from the Mac desktop and it auto-mounts the next ISO from your SD card. When it gets to the last ISO, it goes back to the beginning. That is super useful. Of course, the MacSD mounts drive images too, and this is easier than the SCSI2SD because you can copy the images back and forth to your PC as easy as dragging and dropping. (Don't leave them on the SD card and change the disk images directly, that tends to corrupt the image.)
BlueSCSI: you cannot beat the price and the ease of use. It is perfect for buying one and installing it internally. It's not so expensive that you'd want to use it on several classic Macs just to get your money's worth. If you like soldering and can assemble on from a kit, it is even CHEAPER. You really can't beat the price. It has most of the convenience of the MacSD as far as copying images back and forth from the SD card on a PC. But it does not have that awesome round-robin CD-changer-like function.
RaSCSI: while I haven't had the best luck with my RaSCSI's, they are by far the MOST CONVENIENT. The killer feature the RaSCSI has is that you can connect the Raspberry Pi part of it to your home WiFi network and then call up the RaSCSI's web interface in a browser to manage all the images on the SD card, mounting and un-mounting. You can even copy/paste a URL into the RaSCSI's web interface and it will download the linked file from the web and create an Mac friendly ISO image containing that file and mount it as a CD. That is amazingly convenient. You can create a new disk image on your PC, transfer it to the RaSCSI over WiFi and mount it via the web interface - all without needing to remove the SD card, or reboot the RaSCSI, or disconnect anything. (You'd have to reboot the Mac, of course) Also, I have not tried it, but you are supposed to be able to share the Raspberry Pi's network connection over the SCSI bus with the host Mac. I've read that this is still in development, but there are several people that have it working. If you want wireless file transfer between a modern computer and your classic Mac, this is the easiest way to do it.
Zip drives: as you noted above, the SCSI zip drives can be very expensive on eBay. If you're patient, you should be able to find one for about $40 US. But you have to be patient (and I'm sure you'd have to wait until after the Christmas market dies down). In my experimenting, the zip disks are one of the most reliable and easy methods of transferring files - if you have a modern Mac that can write to a zip disk. If all you have is a Windows machine, then it gets more complicated. I also seem to have the least difficulty as far as SCSI bus termination with the external Zip drives, so take that for what it is worth.
To me, if you're only planning to have a single classic Mac, and you don't want to buy a bunch of different tools, I would get either the MacSD or the RaSCSI. (By the time you pay for an assembled RaSCSI board, a Raspberry Pi 4, and some kind of mount or case, cable, and power supply, the RaSCSI and MacSD be around the same price.) You can save some money if you assemble (solder) the RaSCSI from a kit, or if you bump down from a Pi 4 to a Pi 3B+ or Pi Zero. The Pi Zero is definitely cheapest, but also the slowest. The SCSI speed difference between the Pi Zero and the Pi 4 RaSCSI is about 20%, but that's on a Quadra 840. I don't know if the SCSI bus on the SE is fast enough to allow the Pi 4 to be an advantage. A side bonus of using a Pi Zero is very little heat. Pi 4's run hot.
Lastly, there's the question of internal install or external. If you love to tinker, get a case, power supply, and a SCSI cable and use the MacSD or RaSCSI externally. You'll be able to quickly get to the SD card and make changes and quick transfers from your PC. Believe me, it's no fun at all to have to disassemble your Mac just to get to the SD card, just so you can move a few files you just found over to it. In that regard, the RaSCSI wins because you can transfer files via your home wifi network to the Raspberry Pi (and thus to the Mac). But the down-side of the RaSCSI is that I've struggled with SCSI termination with it. I have two of them, and they both are finicky about how they are powered. If you go with an external RaSCSI, be sure NOT to buy a cheap power supply for the Raspberry Pi. While it may appear that the SCSI bus can provide enough power to power up the RaSCSI and the Pi, it is not a reliable device in this configuration. Add a Raspberry Pi power supply for stability.