Lightweight backpack - not expensive

Generally I don't do a lot of hiking these days. I usually get about on a bicycle but i'm going away for a year on my bike and want to do some hikes as i go, including the 2 month AAWT hike. Before i do that one, i'm going to New Zealand south island for a while with my bike and want to do some multiday hikes over there too.
I already have a bushwalking backpack but its an old style heavy thing and wondered if i could find something better - ie a lot lighter but strong enough. since if i have to carry my pack on my bike, that's probably about 2-3 kilos that i'd be better off without. I expect i'll be carrying the full 20kilos of gear on my AAWT hike, and possibly even a bit more so a strong pack is going to be good there.
Then there's the other factor. Cost. I'm not rich and I have so much other great that i still have to buy for my tour.
So could you please recommend some brands and models that might be suitable and or places to find a bargain and also maybe any traps to avoid.
Thanks!
I already have a bushwalking backpack but its an old style heavy thing and wondered if i could find something better - ie a lot lighter but strong enough. since if i have to carry my pack on my bike, that's probably about 2-3 kilos that i'd be better off without. I expect i'll be carrying the full 20kilos of gear on my AAWT hike, and possibly even a bit more so a strong pack is going to be good there.
Then there's the other factor. Cost. I'm not rich and I have so much other great that i still have to buy for my tour.
So could you please recommend some brands and models that might be suitable and or places to find a bargain and also maybe any traps to avoid.
Thanks!