Those are great little guns; I got one in a trade a couple of years ago, and put quite a few rounds through it before a friend talked me into selling it. For general-purpose shooting with any .22 rimfire rifle, I'd recommend a fixed-power scope with 4x magnification. Click these links to see the specific models I'd suggest:
You don't really NEED a variable, but if you WANT one, I always tell folks to NOT buy a cheap one. Variables have too many moving parts to expect good performance from the least expensive models. Both Weaver and Leupold make 2-7x variable zoom models that are in the same price range as their fixed 4x scopes:
and these will provide reliable performance, unlike many of the lowest-price variables. Of course, you'll also need scope mounting rings, sized to fit both the scope and the base (grooved receiver, in your case, if I remember correctly) to mount any of the scopes listed above.
I currently own, have owned in the past, or have a buddy who owned/owns, all of the above scopes. You can see a photo of the gloss-finish version of that last Leupold scope (2-7x variable) on my Ruger 10/22 rifle in the HandGunForum.net Rifle Photo Gallery. Great glass for the price, in my opinion!
(I am not connected to the SWFA company in any way, but I have bought from them in the past, and would happily do so again; I find their website layout to be very descriptive and easy-to-use, thus the links, above)