10-200 USD or so
You go to the Ruger website, Customer Service, and download the Owner's Manual. There are also several Youtube videos on this.
Sturm Ruger still makes magazines for that pistol. They are the same ones used in their MK I variant and have a 9 round capacity. The subsequent variants, the MK II and MK III . They can be purchased on-line at the Sturm Ruger website, and are commonly available at gun shops.
around 200$ higher depending what condition its in
Insufficient information to answer this question. You would need to provide a model number, and it would help to define if you meant "semi automatic", or if you were referring to a transferrable Class III weapon. Ruger has made several self loading firearms, both in the pistol and rifle class.
For this particular pistol - Mk I, Mk II, and Mk III - it is highly recommended to let a professional handle this. Many reassembly mishaps have resulted from DIY-ing it with these pistols.Contact Ruger Customer Service at the website, get an owner's manual.
In brand new condition they are worth about $280.
Manuals are available at the Ruger website. However, if you've never taken this pistol apart before, I would very strongly suggest you take it a gunsmith and have them show you how to disassemble and reassemble it. Many people find the Ruger Mk. I, II, and III pistols a bit complicated, and the best way to learn is to actually be there, hands on, with someone who knows how.
Magazine
50-250 or so
If it's a .22 Ruger semi auto pistol, it's probably a Mk. I, Mk. II, or Mk. III. See related link 'Sturm, Ruger & Company'. On the left side of that website, there'll be a menu of their products, including their rimfire pistols. Click on 'Rimfire Pistols', and you'll see a drop down menu which will have their rimfire pistols, including the Charger and Mk. III. The Mk. I and Mk. II are simply older versions of what the current Mk. III is.
Cheap and quality are a contradiction. My suggestion for a REASONABLY priced .22 pistol would be a Ruger Mk III. These are going for about $250 on sale. The Browning Buckmark is another good quality handgun for a reasonable price.
Ruger made a MK III, not Remington.