I heard Illinois is planning on raising the tag price to around $500. and go back to selling over the counter due to problems that occured with there tag sales last year. I think it is still just a proprosal though? Here is a link I saw on another site that suggests/talks about the price increase.
CLICK-HERE
As far as it being illeagle to transport a firearm into Illinois without a permit... You are correct. But I have never attemted to get a permit, I just go hunting. The also have a law about how much cash you can have on you while traveling through Illinois. If over a certain amount ( $1000 I think?) They can confiscate it, without charging you with a crime. But I heard there is a lawyer fighting that law...maybe it got changed? Illinois does have some screwy laws, if you behave though you should not have a problem