most of the 5teen series remingtons (510, 511, 512, 513, 514, 521) are going for about $200 to $300 right now. There has been a big surge in the old Remington and Mossberg rifles. Some models will bring more money like the 513-T US will bring more than a 511-X. As more and more people figure out that for $300 they can get a great looking rifle that will out shoot many of the $500 22lr on the market today.
I have 2 a 511x and a 511/513 mashup. They are both tack drivers and will shoot right around 1/2" 5 shot 50 yard groups all day anyday. They are well ballanced rifles that offer so much to a shooter.
Check out Rimfirecenteral.com there are some hardcore Remmy 5teen fans over there. They have a sticky on the top of the remington forum with all the date codes.