New Mac, Lots of Photos, Migration and iCloud Drive Not an Option

Hello, looking for some suggestions. I need to backup my photos from my iMac before I erase and sell it. I have a new Macbook Pro with a 256gb drive, but my photos library on my iMac is over 200gb, so using migration assistant to move my photos library to the new MB Pro is not an option.

Then I figured I would move them all to my iCloud drive so I bumped up my plan to have enough storage, but when I turned on iCloud photo library to copy all my photos there it kept timing out after 8 hours or so of uploading the photos. I am guessing even without timing out it would take days even with Brighthouse lightning internet.

So now I am thinking just get an external thunderbolt drive, move my photos folder from my iMac onto it, and then use that drive to view those photos on my MBP. I figured maybe I could put the last two years worth of photos onto my MBP, and leave everything else going back to 2002 on the external drive.

One other option I guess is to upgrade my MBP to a 1TB drive and move all the photos on there, which would be a lot more money than just getting an external drive.

Any other suggestions or ideas? Thank you.