Some may balk at £50-£70 whilst others think it a bargain, I happily once paid £150 for one which is a sky high absurd price to many people, but no more than going out money to myself as I'm financially able to indulge myself nearly without limit for things I want regarding my hobby with the price paid being of no concern. I wanted it, I bought it and still have it to this day.
As I say it's what it's worth to the individual and on a good day that type of individual may read your ebay listing.
The best person to ask here is lardo who does a lot of back and forth with all things zeddy including I believe some Memotech keyboards and has a better understanding of how much gear is selling for.
At the moment there is a zeddy with some kind of home grown keyboard monstrosity attached and they want nearly £200 for it so a Memotech would look very attractive next to that I would have thought.
https://www.ebay.co.uk/itm/233394013826 ... SwNq9dxEYH
It was not in perfect condition with the paint being part rubbed off on a number of keys.
As ever with eBay or similar it is luck of the draw what you get on any given day though. You could start an auction at £100 and see where it goes (and have a pretty good chance of a quick sale) or start it a bit higher and it may take a bit longer.
Mine was listed at a fixed price. I have had very hit and miss results with auctions.
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA