How much 'discovery' does a patent require in order to be worthwhile?

We have been advised by a patent attorney that our product design is patentable and that we can apply for a provisional or full patent. Additionally, we have been advised by other entrepreneurs that a patent is only worth the amount of discovery that's put behind it. Their view was that this discovery phase (carried out by the patent attorneys) should cost at least $100k Australian Dollars to be worthwhile, otherwise you may be patenting something that already exists in the world either as a patent or otherwise. Can any patent specialists shed further light on this for…