Quality photog backpack for Haiti trip?

I'm going on a missions trip to haiti this summer and am looking to buy a nice backpack to carry all of my gear in. I'm taking a nikon d3100 body with a grip, the 18-55 kit lens, 55-200, 35mm prime, and other small stuff (hoods, filters, batteries, and some personal items)
I'm hoping to spend less than $150.00 on it and I'm looking for a backpack that will provide good security (while I'm wearing it/if I ever were to take it off--don't plan on that), enough space for everything, relatively small(carry-on size), and water/weather-proof.
I understand that it is kind of a big order for so cheap but hopefully someone can help!
I looked at the lowepro flipside 300 and LOVED it but after doing some research I found that it wouldn't fit my camera well with the grip on it.

Have a look at the military style backpacks…

I prefer this style because it doesn't attract attention… No-one knows it's camera gear that's inside it…

I use a few different bags… This is my favourite and i've used this for over 10 years and it looks as though i'll get another 10 out of it…
http://www.ebay.co.uk/...1152812325

This is the style of my other bags… These bags have the advantage of using the molle system that let's you add extra pouches to your bag for more kit… It sort of lets you customise your bag…
http://www.amazon.com/...zon.com/s/