We're leaving on a two week trip to Mexico in a few days and as part of my preparation, I did a lot of looking on line for an economical camera backpack. My pick was one that Amazon is marketing under their own brand. Other than the zipper tabs, there is no other advertising logos on the pack. The cost was just under $35.00, and after looking it over it seems to fit my needs. There's so much space I told my wife I have to go buy more camera "stuff". Those who are married know how far that went. There's serveral padded compartments that are adjustable with velco dividers, additional pockets inside and outside the main opening flap on the backpack plus two small pockets on the sides of the pack (one which is covered by the tripod if you have one strapped on. Here's a photo of mine, packed and ready to go. (Truth in posting: Had to use wife's Nikon as my K-x is in the bag)
Will be field testing over the next couple weeks and will report back on how it's working out for me. If you want more details just search Amazon for "AmazonBasics Backpack for SLR cameras.