I presume the best value old stock metal tape to be the TDK MA-xg?
I found a few in stores as recently as 3-5 years ago.
If I wrere to go on ebay, how ,much should I expect to pay for a old stock sealed MA-XG? Any oythers worth scouting? Perhaps the Realistics? Denon?

They are selling for £15+.

Sony Super Metal Master are fetching more so I think they may be worth looking out for.

got sealed 60 and 90 GOLDSTAR metal (80'ies cassettes, equivalent to TDK MA-X), will sell for good offer (i'm in germany...)