The Sandisk SDCZ880-256G-G46 costs £ 105.99 on amazon.
The DIY variant (enclosure, cable, SSD) costs:
Enclosure -> XT-XINTE SS25490-SS25491 : £25.50
https://www.amazon.co.uk/dp/B07FR6VMS8
Cable -> Belkin F2CU052bt1M-BLK : £24.72
https://www.amazon.co.uk/dp/B073KCPS2M
SSD -> Samsung MZ-V7E250BW : £79.99
https://www.amazon.co.uk/dp/B07CGGNX7S
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Total: £130,21
It is probably cheaper, if you buy the same items from other, reliable sellers.
And this DIY variant is up to 2 times (100 %) faster than the Sandisk SDCZ880-256G-G46, if your Mac / computer supports USB 3.1 Gen 2 (10 GBit/s). Or in other words, the DIY variant provides up to 100 % more performance and is only ≈ 23 % more expensive than the Sandisk SDCZ880-256G-G46.