Good question.
I'm not the traditional comic buyer. I focus on Star Wars and Transformers for the last couple years.
Price per comic for IDW is about $4 each while Darkhorse is more like $3 each. Generally you can subscribe to whatever series you like at a comic shop and get a 25% discount.
That basically covers the exchange from the USA now, though it was way better when out $$$$$'s were at par
Both Star Wars and Transformers seem to focus on smaller story arcs that one could get into without knowing anything else about them. I don't know how the superhero books work though.
One route to go if your looking to get into an established series would be to get the Trade Paperbacks. These are books which incorporate 5 or 6 comics from one series, generally in order of release.
Thats all I can offer. I'm sure someone else might have more info than that though.