No, you cannot use salt water for contact solution. Salt water consists of sodium chloride, which is pungent chemical composition to eyes. And using salt water to soak the contact lenses cannot perform the same function as the contact solution such as it has no effect of cleaning and sterilizing the microbes and dislodging the protein on the contact lenses. What's worse, it is harmful to the contact lenses, it can do great damage to the constituent of the lenses and give rise to the dehydration of the lenses, which will shorten the usage time of the lenses. Besides, it will do harm to the cornea. So I advise you to buy a bottle of contact solution as soon as possible.
Well, it seems that you would like to use salty water as an alternative for contact solution on a temporary basis. So, in theory, it is plausible, but after soaking in salty water, you still have to use fresh water to wash the contact lenses before wearing them. Anyway, I find this approach very difficult and time-consuming, so I still recommend that you get a bottle of solution, which does not cost a lot.
If there is no contact solution, salt water is the best alternative. A small amount of salt water will eliminate more bacteria than if you use plain tap water. However, you cannot use it for a long time. It is not recommended to use any of these remedies long-term, and you had better use regular contact lens solution.