You don't need to buy those full long piano keyboards. Those are meant for professional piano players. Buy the medium size piano keyboards and they are not that expensive around $200 to $400. If you want to compare Casio and Yamaha, then you need to know that Yamaha beats Casio in a lot of ways. The sound coming out of a Yamaha piano keyboard is much better than the Casio ones. Casio may have a lot more features and extras function but you don't require them if you are just starting to learn to play piano keyboards. Yamaha has quite a good amount of features too and these features are enough for starters like you. When you get to a certain level of expertise then you can buy a better brand instead of Yamaha. There are other brands which are better in sound quality but Yamaha will do good for beginners.