Wondering why 35Ah alternator for yanmar yse8 is so expensive? I been asked 400 bucks. You can but 145Ah car alternator for 250 bucks!$
On ebay, they are a bit cheaper but still 300 bucks without warranty...
I sm still in shock!
Have you had an auto-elec place confirm your existing one is unable to be repaired?
It costs an incredible amount of money to take the "Yanmar" stamp and apply it to the box. Much more expensive than the "Toyota" or "Holden" stamp.
Google around and find what manufacturer and code the alternator is. I understand that most of them are just rebadged units from other manufacturers and therefore can be bought much more cheaply without the Yanmar sticker. I forgot how much my "non-genuine" starter motor and alternator were, but they were much cheaper than the branded version.
Take your old alternator to a wrecker specializing in Japanese cars (small ones).
Drop it on the counter and ask if he can match it.
There is nothing Marine about these units except for the price.
gary
As has already been said, find yourself a good auto electrical repair shop and drop it in to be checked and repaired if needed. I know a good one at Taren Point however probably a bit far for you. 
This is the alternator you need. Don't go above 35 amps. Find a reseller in Australia for the Chinese alternator. Should be $180-200 posted to your door. The quality of these units is impressive.
www.ebay.com.au/itm/274857143658?hash=item3ffec32d6a:g:sNUAAOSwYDZg4yED
