Ok, so here's my take:
In the Midwest, either pants or skirt work for everyday suit occassions, but I personally would only wear a pantsuit if it was snowing-ly cold. Skirts suits are more accepted.
Good places to buy them:
$$$$: D&G, Brooks Brothers,
$$$: JCrew - they have outlet stores - any outlet JCrew is a good pick;
$$: Macys - my favorite suit came from here; Express, Limited, other big department stores
$: Gap, for seperates; the Issac Mizrahi line from Target
Also, I have had great luck at secondhand stores, and even Sal Ar and Goodwill, especially those in nice neighborhoods. You may need some tailoring, but its worth it.