Yes, apples and oranges. the Ruger Old Army 5.5 fixed sighted revolver is 'rare'. The 7.5" Old Army is way more common. Can't compare prices with the Vaquero.
Since in Vaquero land, there are more 5 1/2 and 4 5/8 barreled revolvers, the 7.5" might be valued more.
That said, if one indeed ran into an Old Model Vaquero, that would be very rare as there was none manufactured to my knowledge
. The original Vaquero and New Vaquero are both New Models (not pre-73", two pin with transfer bar). FWIW, .44Mag will always be found on the large frame regardless.