I'm going to try and figure out my breastfeeding costs here, just for fun.
-Medela Harmony Hand Pump: FREE from WIC
-New Medela Swing Breast Pump: $30 (Purchased from LLL- it was a Silent Auction unsold item)
-Pump Bags: ~$15 so far? (I don't really pump much.)
-Born Free Bottles: FREE Gift Set from Baby Shower
Total Pump-related costs: $45
-Nursing Bra: FREE from WIC
-5 or 6 nursing tanks: ~$100
-Nursing Pads: maybe $50?
-Sleep Bra: $15
Total Clothing-related costs: $165
-The Womanly Art of Breastfeeding: $12
-LLL Membership: $40
-Lanolin: $5
Total Support/comfort costs: $57
Am I forgetting anything? I don't think I am so... TOTAL COST (to this point): $267
DS has been around for 228 days so far averaging out to be a cost of $1.17 per day. If I buy nothing else and he is breastfed for one year the cost will be $0.73 per day. If he is breastfed to my goal of at least two years and I renew my LLL membership ($40) bringing total cost to $307, the cost-per-day will work out to being about $0.42/day. Not as low as the article but still pretty dang cheap.

I realize that some people have more expenses and some people have next to none. I consider my spending to be fairly average, middle of the road.
While there are many reasons to breastfeed and ideally cost shouldn't figure into doing what's best for your baby, I don't think it is wrong to market cost as a benefit.