The higher the capacity the more you'll save by going M2 + Enclosure. I picked up a 4tb M2 and Ugreen enclosure last Black Friday for a combined cost of around £160-170 IIRC. A comparable external SSD would have been well over £100 dearer, if not more.
If you're looking for something smaller like 500gb or 1tb then for all the savings you'd make (if any) you'd be as well just buying a dedicated external drive.
Having typed all that I just see you were looking for 2tb - I'll leave what I wrote though in case it's of use to anyone else.
At 2tb then it gets even muddier. A quick browse suggests a 2tb M2 can be got for around £100 - adding an enclosure at you're looking at around £120 all in.
Conversely, I can see SanDisk drives for £135ish.
I will caveat all this by stating I'm not comparing drive speeds etc - if those figures are important then that will of course have a bearing on price.