Prices are per square kilometer, but there's a minimum order of 500 square kilometers, and you're paying for a licence for a certain number of people to use them in a certain way.
TLDR: best have at least a few hundred dollars handy even if you're only wanting to look at one city.
A lot of lower resolution satellite data is free and open though
http://www.landinfo.com/satellite-imagery-pricing.html
Prices are per square kilometer, but there's a minimum order of 500 square kilometers, and you're paying for a licence for a certain number of people to use them in a certain way.
TLDR: best have at least a few hundred dollars handy even if you're only wanting to look at one city.
A lot of lower resolution satellite data is free and open though