Depends on how serious you are. Our first piano when my son was a beginner was a refurbished one for about $2500. After losing it in Katrina we bought a new Kawai upright for about $3500.
If you want to save a bunch of money, Casio makes some decent 88 key digital keyboards for $400-1000 and up. We bought one for about $700 a few years ago at Guitar Center to have something portable. It has speakers on it or can be plugged into an amp. They even make them with "weighted keys" to feel like a piano.
If you're taking piano lessons, you absolutely need 88 keys at home. Don't buy a smaller keyboard.