Penfolds Grandfather port is indeed quite nice (also circa AUD 100 per bottle); even better is Greatgrandfather port but at triple the price. Ports have a huge range of flavours and quality, and Australian ports are significantly different from Portugese ports. There is little correlation between price and quality (more expensive port can be worse than a cheaper one). Currently out of fashion so pricing is good, esp. for mid-range products (10-20 year range). Quite stunning price/performance is the Seppeltfield Para port (has the same subtlety as Grandfather port but at $20/bottle, so 20% of the price -- obviously not as good, but quite enjoyable). Also good are Penfold Bluestone. Bad (to my taste) is Galway Pipe (too sweet and syrupy and lacking depth).

If you are serious about port, try a good (any vintage) Fonseca; it will open your eyes as to what is possible (as well as drain your pocket book).