Adobe Illustrator CC 2015 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Illustrator customer). Adobe Illustrator CS6 is still available for purchase (without a monthly plan) if you prefer.
Adobe Illustrator CC 2015 is the industry standard vector-drawing environment for designing across media. Express your creative vision with shapes, color, effects, and typography. Work with speed and stability on large, complex files, and move designs efficiently among Adobe's creative applications.
Note: Now requires OS X 10.9 or later.