It really depends on what level you plan on doing! I've showed from backwoods to AA circuit and spent anywhere from $40 to over $2000.
It depends on the level and type of show
It depends where you are and what shows you want to enter, along with if you already have all the stuff to show. I live in Canada and show around Alberta, Saskatchewan and Manitoba and my entries can be anywhere from $250-$1000 and those are the cheep shows. You also have to consider the trailering fees to the show and the hotels if they aren't near your house.