Well I am new to this and not sure that this is really a profitable endeavor given recent crash in bitcoin, but I would invest 500 USD or so to see.  I was thinking about the  Hex Fury from ASIC which does 11 GH and is currently available. The bitmain look better but are all sold out and no prices are available.
So happy for advice on how to start a bit of fun and profitable mining for 500 or so.