Sure but the city of Chicago isn't very expensive. It's cheaper than the suburbs of say DC or NYC or SF by a good margin. $70k is a very good salary in the city. You can get a nice 2BR apartment in Lincoln Park (one of the more expensive areas) for only $1,600 per month. My studio Westchester costs almost that much!
Chicago teachers start around $51k with a bachelors. You can live better with that salary in Chicago than many Googlers earning $100k trying to live in SF...
Where are you getting your data? I just moved from Chicago last year and my friends in Lincoln Park were paying around $1600 for a 2BR at Clark/Fullerton. Trulia suggests that this is not uncommon: http://www.trulia.com/for_rent/Chicago,IL/16_zm/41.920751,41...
Also, the average for places like Lincoln Park is skewed up by all the high-end housing in the area. Places like Andersonville and Edgewater are even cheaper, and very safe and family-friendly: http://www.trulia.com/rental/3102177710-5406-N-Kenmore-Ave-2...
Heck, last year I was paying $1450/month for a 1BR in a full-service high-rise in Streeterville with a 28th-floor view. My wife paid just around $1100 a month for a huge 1BR in Streeterville a couple of years ago. If you've got a roommate, it's totally possible to live in River North on a teacher's starting salary.
I paid 1600 for a two bedroom 1100sqft apartment in a nice area(wicker park) in 2011-2012. With no need for a car or car insurance it was more affordable than I expected.
Chicago teachers start around $51k with a bachelors. You can live better with that salary in Chicago than many Googlers earning $100k trying to live in SF...