@Zhnyaka, as Antje says, cabbage - any kind - and onion make a great base for other ingredients. Even better if you can add a squeeze of lemon juice either while cooking or at the end. The kind of sausage you can get depends on where you live - in UK sausages are usually fairly high carb and if you hunt around and get lower carb ones, they tend to be more expensive. Continental sausage is generally lower carb because it's normal not to add a starch to them like we do in UK. But you don't need much sausage to make the cabbage and onions tasty.
Streaky bacon is pretty inexpensive and it makes for a very tasty dish as well. If you shred the cabbage and onions (maybe in a food processor) and cook them gently in butter, they cook down to a very tasty base. You could make this as a base and add whatever ingredients you want to it - bacon, sausage, grated cheese, cream cheese, tomatoes (cheap ones chopped in tins will do fine), tomato puree, even some minced or chunks of meat that you enjoy. As long as you season it to your own taste, it will make a good meal.
You can buy low carb pasta, but they tend to be expensive and if you are like me, you can't eat them anyway (they contain fibres from plants I can't tolerate) but other people can.
Then again, you could try making large quantities of something you enjoy and keep it in the fridge to use over the next 2 or 3 days, or in the freezer to take out when you want it.
You could make a fairly plain soup (like the one Antje made a day or so back) and add things to it on subsequent days (bits of sausage, bacon and so on or chunks/slices of vegetables).
There again, you could just have a stock of cold meat and/or cheese/ smoked, cooked or tinned fish that you can snack on with some lettuce leaves to wrap it in. Soft cheese and chopped ham mixed together and wrapped in lettuce, is pretty good and takes no time at all to put together.
Spinach leaves take no time at all to cook and are great as a base of some fish or mixed with soft cheese and used to fill a lettuce leaf.
Maybe you could find a few different bases you like - like the cabbage or the soup - and use them over a period so that you don't get bored and have bits and pieces to add to them as required.
To be honest, there are lots of days when I am too tired (lazy?) to do any food prep and I often don't feel like eating anyway so on those days, it's good to have something in the freezer that can be pulled out and shoved in the microwave if I do feel the need of some sustenance.