There's really no telling. Anything from +4000 USD for a custom build to a couple of hundred for a used, entry-level bike.
Normally, two. There are usually only two seats on a tandem bike.
A tandem bicycle.
a tandem
Tandem bicycles are bike designed for more than one rider. Brands that offer tandem bikes are Co-Motion cycles, KHS Bicycles, Santana Tandems and Trek Bikes.
Bike rider, randonneur.
You're probably thinking of a tandem
how much would it cost you for 2 houres on a velbil bike
it costs about as much as a bmx bike or more
my thruster bike cost is $80
The one who works the hardest.
A good race mountain bike would cost you about $6,000 to $10,000
Usually, yes. But a true tandem will have two sets of pedals as well. There are a few bikes that can have two seats w/o having two pedals, these are usually considered cargo bikes instead.