Galaxian for the ColecoVision seems to be off:

http://www.digitpress.com/DP/cmf/game.cmf?gameid=9478

Especially when compared to Jungle Hunt:

http://www.digitpress.com/DP/cmf/game.cmf?gameid=9541

It's been my experience that Galaxian does in fact show up more often than Jungle Hunt, but not overly so. $15 is far too low a valuation for the game.

I'd suggest minimally bumping up it's value to $20. Maybe that's enough.

However, if I had to speak my part, I'd bump the value to $25 and raise the rarity one notch from R4 to R5. This still places it below Jungle Hunt (R6/$30), but properly distances it from the more common Atarisoft titles of Defender and Centipede (both R3).