New Job Offer: Is salary enough for life in Paris?

30,000 Euro per year ain't bad for a 27-year-old living in Paris, trust me. In many cases, even locals have trouble landing a permanent job until they're into their early 30's.

Keep in mind though that about 21 to 24 percent of your monthly salary gets docked for social security and pension - which means you're entitled to a fantastic healthcare system. 

Furthermore, you can count on forking out about 800 Euro a month, for accommodation - of course, the limit is really the sky, in this regard. But, 800 Euro will get you a one-bedroom in a decent place. Just try and find a flat nearby to the train line you'll need to take to get to work, as this can greatly reduce your commute time, and the attached stress-levels. 

FUSAC is a good place to start looking for rentals. 

Regarding the work permit question. Unfortunately, you're initially bound to the employer who sponsors your visa and the residency permit (carte de sejour) you'll need to get to live in France for more than a year. You'll have to renew the residency permit annually, and the renewal requires that you're details are still the same as when you initially filed (so that your sponsoring employer is still the same). 

Thus, if you change jobs, you'll have to theoretically re-apply for a visa (long-stay category D) and the permit, which may mean you'll have to go back to the States during processing. Though, I'm not sure if there's a loop hole or a way around this.