brokerage will be on buying and selling. no monthly charges will be there. Normally 1 unit of gold etf will be equivalent to the cost of 1 gm of gold. (except Q-gold which is of 0.5 gm denomination). Cost of each unit will vary from 2520 to may be 2800. I think reliance gold is costing around 2520. HDFC, etc may be little more.
1 unit of gold etf can be converted to 1 gm of physical gold in some places like Mumbai, Ahmedabad, etc, after paying some % as conversion charges. In other places, so far, this facilitiy is not available. However, u can sell in open market like any share.