Sharma, hi. Because each and every didg, is made out of different wood piece, there are many lots of levels. You may found hand made (Bamboo, Tik wood, Agava Cactus) digedridoo`s, from 50$ up to 250$-300$, these kinds would be good for learning how to play a didg – and some of them has a really good sound and vibes. 

If this instrument catches you, and you want to get more serious, I would recommend you to buy a genuine Australian didg, mad by Termites, out of Eucalyptus or Red wood – in my own opinion – they have the best sound and back pressure, you`ll find them between the prices of 100$ - thousands of $ for very special instruments.

If this is only your first encounter with the instrument – I would take a plastic tube (for such as electricity or for watering), with about 3-4.5CM diameter, and start with it, you’ll be surprised of the why these tubes sound.

If you have any more questions regarding that subject – this is my specialty, don’t hesitate to ask me.