I own a 76 key Yamaha keyboard. Realistic sounding instruments(in fact the best I have heard for the price). Its about $300-$400.
I had a keyboard before it which was the normal size but I ran outta keys on some of my songs, so I would go with this one if you don't want to spend too much(I play on a baby grand when I really want to play)
Heres a link to similar ones:
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