Waterfield cases and bags are SOLID. I have been using them since about 2007, and they have been awesome.
I currently own a MBA sleeve case, which is new. And also I have had my iPad 2 sleevecase since a week or two after the iPad 2 launched (When they got them in stock). They hold up very well and are very durable.
For the bag, I have the Vertigo bag, and I don't remember which size (but I think I made sure it fits a 13" Air) but it was around $100 (+/-$10) when I got it in 2009.
I used to own a bag and sleeve case for my 1st gen macbook air (which I sold along with the MBA) and I used them heavily for school for a long while. When I sold them, the case and the bag still looked brand new. The ballistic nylon they use for their stuff seems to be very durable and easy to take care of.
Their stuff is quite expensive but from my personal experience it is worth every penny. Also, their service is great too. When I got the iPad 2 case it didn't fit right so they sent me another one and let me keep the first one (which my wife now uses to store her kindle).