Getting hold of an RM850

Further to the previous thread, after some research and no small amount of help on this forum, it seems like the RM850 would be the best bet to replace my old TX850W. Not completely clear as to the difference between the RM850 and the RM850X or RM850i, but from what I can tell any of them should serve as the replacement I need.

That being said: since ( finally ) arriving at that conclusion, I've struggled to find one at anything less than second-mortgage prices, and for some reason this seems to have magically changed in the last couple of days. There was one on Amazon for £125; now the cheapest one on there is £225. There's one on the Curry's website for £125; Curry's themselves, however, tell me on the phone that there's no stock showing at any store in Kent, they won't post from stores further afield, and you can't order it online.

I'm really starting to tear my hair out with this now ( and I've got a lot of hair ). To be honest, I already had kittens when I saw the price was £125, never mind approaching twice that! If anyone can point me to a good, sensibly-priced, reliable resource for one of these ( and / or if anyone can tell me whether the X or the i model would make any difference ); or indeed, for that matter, if anyone knows where I can actually buy a replacement for the original TX850W at a price that won't involve selling my car, I would really appreciate it!

I've heard that PSUs are in high demand and low supply after the global pandemic started. I found the RM850x for £139.99 at Scan. If it's not too expensive for you, maybe just grab it quick?

https://www.scan.co.uk/products/850w-corsair-rmx-series-rm850x-full-modular-80-plus-gold-sli-crossfire-single-rail-708a-135mm-fan-at