Ultimately, the value is depending on the condition and the amount of stuff supplied with the plane. My 044 was something like 45GBP no shipping, in original box, great condition.Which, as it turned out, was because it wasn't used, the plane iron did not protrude past the skate, so it kept on fouling one side of the groove, fixed it with a file and it is great now. Also bought a Stanley 50 which came with an additional 044 for 30GBP together, but that one is in a much rougher condition, no box, some pitting, somebody buggered up the threads of the iron clamp on the 50 so drilled right through and fitted a regular screw, that sort of thing..... My 043 was about 30GBP, pretty good condition. And I have a 044c which I converted into a kerfing plane (same idea as the Quangsheng 043), which was 25GBP or thereabouts.
You can get lucky on an auction which does not see a lot of action, or get lucky on a newly listed "buy it now" (on eBay), or somewhere reasonable in the middle. Step away when an auction turns silly, a bit of patience goes a long way
Gotta say though, I am in NL so we always get another 15-25GBP shipment..... Must be great to just visit a car boot sale in the UK and find a nice plane for 15GBP, metal planes are not so prominent this side of the water, lots of wooden planes.