Depends on how high-end you need the keyboard to be.
I got a Casio for my daughter a few years ago from Best Buy (online, shipped for free) for about $200. I had to buy a stand for it and a plug in sustain pedal separately, but that only added about $40 to the cost. She doesn't sit when she plays, she actually prefers to put the stand tall and stand up. (She is 10). She is in her 3rd or 4th year playing.
The one I got is just shy of all the keys (I think it has 76 instead of 88 keys?), but the keys are weighted and pressure sensitive, so she gets a pretty good "real" feel when she plays it. It was a great "investment". We gave it to her as a Christmas gift also. :)
btw, I bought another one exactly like it from a different retailer for our church about a year later. The price was the same but for whatever reason it didn't come with a power cord. (Mine did, right in the box). So that had to be purchased separately.