The cheapest way to lighten your pack is simply to take less stuff. Start to think of items that can fulfil two purposes for example. The obvious one here is to have a cooking mug - use it for cooking and drinking, Alpkit offer some good value Titanium cooking mugs. Another example would be for travelling in the warmer months: don't carry a warm jacket for the evenings, just climb into your sleeping bag at the end of the day.
For a stove I'd go for something simple and gas powered. A freestanding stove which connects via a flexi hose to the gas canister is a good option. Get one with a pre-heater then not only will you have a low centre of gravity (a failing of all the trendy Jetboil like systems) you will also be invert the gas canister in cold weather and run on liquid rather than vapour which may not evaporate well. Once again I'd recommend Alpkit - I wrote a review of the Koro stove here >>
https://westonfront.wordpress.com/2019/09/01/lightweight-stove-review-alpkit-koro-mytimug/You also ask about sleeping bags. I would suggest that you simply cannot beat a down bag from Rab. Their quality is second to none, the zips don't snag and whilst they are not the cheapest, neither are they the most expensive make out there. For summer use I find the Neutrino 300 absolutely superb. They also offer women's models which are slightly shorter in length but with a greater amount of fill, so you end up with something warmer at the same weight. For info on the Neutrino 300 see
https://westonfront.wordpress.com/2020/07/27/rab-neutrino-200-ultralight-three-season-sleeping-bag-a-review/Water - consider using a bladder and a water filter. If you are able to harvest water regularly you will need to carry less of it. By using a water filter rather than iodate tablets you can drink the water instantly, not wait 30 min for the chemistry to happen. Also the water tastes considerably better. I'd recommend a small bladder and a second one you can fill in the evening to have enough water to cook with and brew up the next morning. There are not many one litre bladders out there, but I've been very pleased with my Hydrapak Stow -
https://westonfront.wordpress.com/2021/10/04/hydrapak-stow-one-litre-soft-bottle-bladder-a-review/, but be sure to not to get the early model with the colour matching lid, the lid seals on these leak and the newer models have the same thread type as most water filters so you can fit this directly to the bladder.