For the record my dry pack weight is in the 9-10 kg range. This is everything but food and water, it includes fuel, hiking sticks and a lot of "comfort" items such as vacuum flask, GPS, solar battery and an enhanced first aid / repair kit.
As I walk alone, off the popular tracks for several days at a time, I have to be able to cope with what ever happens - good job since the last time out I had a freak accident which nearly sliced the top of my finger off in an area with no phone signal. It took some some serious bandaging to staunch the flow of blood. It was over a day before I could get any sort of medical attention. I've carried the kit for six years and this was the first time I've had to use it on myself - though repairing my kit is a frequent occurrence!
Anyway back to the OP, charity shops can be a good source of cheap kit. I have two rucksacks of 50-55 litre capacity weighing about 1kg which cost £6 each. One in use, the other as a reserve.
The weight distribution in your rucksack is at least as important as the overall weight. In general the higher you carry a load the less effort involved. I also carry my tent externally strapped in front of the top pocket so that it sits over my shoulders. I've added extra straps to my rucksacks to enable this. Also you can pitch the tent without having to open your pack - good in the pouring rain.
The difference in comfort in carrying the tent in that position rather than in the pack is remarkable.
It's worth experimenting with some cord to find what arrangement suits you best while walking.
One item that it's easy (and cheap) to save weight on is your towel. Microfibre is much lighter than cotton and more efficient at drying so you can go smaller too.
If you're into more serious cooking when hiking, other than just pouring boiling water into a bag, then plates/bowls are useful. The black plastic trays from cook in the oven ready meals are free, adequately robust and much lighter than anything you can buy.