Contact Ruger
100-200
You could either take it to a gunsmith or put it on yourself. I had a Ruger 10/22 and I think it had a scope rail for mounting. Should be just a matter of tightening it onto the rail and sighting it in.
175 USD
175 USD
It's worth between $10 to $15 used.
100-425 or so
50-600 USD or so
10-400 USD or so
It is possible But do i need to buy a dovetail, or a mount?
Well, it depends on what you have. The 10/22 comes with a proprietary rail, and is tapped already for a scope. If you have one which isn't, you need to decide what sort of mount you want. You might want to add a Weaver or Picatinny rail, or you might want to mount the scope bases directly into the receiver. Once you've made up your mind, then you get it tapped for a scope.. I'd recommend you leave this to a qualified gunsmith.
50-250 USD or so
Not without some help