Quality grand pianos cost on average $20,000. They also require a large space and regular maintenance. Tunings currently run a minimum of $80 and are recommended twice a year (at season changes). An upright acoustic or an electronic keyboard is a good alternative, although a decent sounding upright costs $5,000. Electronics take up much less room, require NO maintenance, and several excellent models with built-in cases (as a long-term investment) can be purchased for under $1,500. Smaller portable models with features sufficient for beginners start around $300.

From my FAQ page:
Q: Will an electronic keyboard be okay for learning piano?
A: Many of my students have electric keyboards. I myself have a couple Yamaha portable grands (61 and 76 keys) and two 88-key Casio Privias. It's best to buy one with weighted, touch-sensitive keys. I also strongly recommend models with at least 5 octaves and a jack for a sustain pedal attachment. If buying a pedal, I recommend M-Gear (aka M-Audio) brand. They make a sturdy universal pedal for around $20 shaped just like the pedals on an acoustic piano. Auxiliary equipment such as seat, X-stand and power adapter are a minimal expense.