We run our pool from mid-May to the end of Sept. and it costs us approx. $200-400 per year. This includes chemicals, added electricity, and we always add some new "toys" to the mix!
As for filling up your pool, you have to maintain a certain water level or your skimmer basket will suck air. I have a 52" pool and the minimum water level that I must maintain before it sucks air comes to me just above my armpits (mid-chest, pec) and I'm 5'4" tall. Hope this helps!