Hello Bianchi started making the Nyala in 1990 and I am missing my '97 catalog but I do not see it in the '98 one. suntour components componenets would indicate a '90/91 bike. shimano 200gs with thumb shifter started in '92 the Nyala ( an african antelope btw) was second from the bottom of the line of Bianchi ATBs from the few prices I have the look to have sold in the $380 to 400 range depending on year.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk