There are cheaper digital pianos, even full 88 key ones with touch response (i.e. softer/louder depending on how hard you press).
Costco usually has an ok selection:
http://www.costco.ca/CatalogSearch?s...&keyword=piano
Unless they've expressed an interest in learning piano might be better to start cheaper (not super cheap, full sized with touch sensitive and weighted keys is still a good idea, too cheap and they won't like it at all), and also easier to get rid of if they don't catch interest than an actual massive piano.
Plus the electronic one is better if they decide later to play keyboard rather than piano, they'll likely be able to either use the extra sounds or plug in boxes to get whatever sounds they want.