Sam
I would firstly consider what you're going to be doing with it / using it for, and secondly decide what your deciding factors will be - ie are you just going to use it for the odd bimble / day out / overnighter; will you be walking a short distance from car to fixed location or travelling over a distance; is image more important than function / features etc.
I have a Sabre 45 and really like its functionality and flexibility (with PLCE pockets & plenty of attachment points). I use a smaller Munro for shorter trips. I would recommend either if that's what you're after, although neither are anything like the Rugged River or Bushwear packs you've mentioned.
There are a large range of sacks out there which will cost anything from a few quid to many hundreds of pounds, although more cost doesn't always make for a better bit of kit. I guess what I'm trying to say is remember you don't have to blow your budget all on a bag, if you find something suitable cheaper, then that means you've saved something to put towards the next bit of kit you're after. I'd also suggest you look at ex-army / surplus kit as this can be very reasonably priced, and sometimes used kit can give you the best of both worlds - it will have the functionality and look the part (especially the older stuff).
I hope this helps.