In the 70s you could buy them from "exchange&mart" for £12 iirc.
I bought one of these gc and still in military guise in the 90s for £300, which seemed like a lot of money at the time. it was tidy and original but the grips and WD tyres had melted
When they reached over £1000 I sold it - ultimately there are 1000s out there so shouldn't really command such a high price.
They aren't very nice to ride, especially with the spindle "pedal pins", and famously the paras never used them (despite the number offered for sale "found in a barn in Arnhem
)
One d-day veteran remarked that if you jumped off the landing craft with full pack and parabike, you sank.
Of course most of them have been kept unoiled in sheds and garages, so this one's condition is far from unusual.
Reaching both military and cycle collectors though helps hold up prices.
Perhaps militaria collectors are less tight