Is there a way to send digital signals over long wires(2-3 m)? Can I use buffers to do so? Is it efficient enough.
Yes. Applying a voltage to one end of a two or three meter wire will make that voltage appear on the other end very shortly after that. If you're not using these digital signals to supply current then you don't really need to worry about the thickness of the wire.
If what you really mean is, can you use two or three meter wires to power an LED, then the answer is still yes, but you need to consider the resistance of the wire. You can measure the resistance with an ohm meter, but in practice it's very likely to be no more than an ohm or two which you can probably ignore.
If you're sending data there is a whole other mess of things you need to worry about. But it appears you're not trying to do that.
of course you can do it... just try to use a wire like awg 20 or less, to avoid the drop voltage by internal wire resistance