Here's my story:
This summer I did the TA and from previous trips I wanted the No-Ad sun screen: Cheap, large bottles, good smell and not greasy. Problem is, that it is difficult finding the No Ad sun screens. I went to Walgreens and Walmart but they don't carry them in their phsysical stores. I ended up buying the Walgreens house brand because it was cheap and "looked" good. I hated it from day 1. It was so greasy and it would never soak in. A few days later I got so annoyed that I went straight into a Walmart to see what they would carry. In Walmart I applied small amount of sun screen (from different brands) to small spots on my arm and started walking around the shop. I was observing how the different products would behave on the skin. An oh boy there was a big difference: I settled with the Walmart brand called Equate, more specifically "Equate General Protection Lotion SPF 50, 16 fl oz" at 8 dollars or so:http://www.walmart.com/ip/General-Protection-SPF-50-Sunscreen/14122653
This one behaved like the good oll' No Ad which I had missed: No greasyness and very cheap.
The bottle lasted for the entire TA, which in my case means 30 days, and there was more left. In general I applied sun screen 1 time a day.
PS: I do hate sunscreen myself - even though I found a good one.