Baseboard lumber choices for staining
If you want to color maple, you might investigate dyes rather than stains - leaves much more of the grain visible.

If you're going to stain it anyway, poplar (in the lumber trade that almost always means tulip poplar) is a nice, cheap, stable wood. Has a somewhat greenish cast, but dark stain will obliterate it. 

Responding to Jack's comment: I've posted this one before - it's from "fowl weather custom birdcalls" and provides a nice sample of what you can do with dyes on maple. I suppose it may be possible to use dyes in a manner that gets less clarity, but my overall experience is that dyes leave more "wood character" visible than most stains do. My personal preference is to let the wood be wood, and use a different wood if I want a different color; but I have seen nice things done with dyes.