I rebrushed the alternator on my 1987 Toyota 4x4 extra cab for about $3.50 in parts and a soldering gun. It too was a Denso. Had 210,000 miles on it when I did it. Had over 320,000 on it when I later sold it. I never ran anything extra electrical on it. Just headlights, fan and A/C. Keep the ancillary stuff turned off as much as you can and the alternator will last a long, long time. Heated mirrors, heated seats, heated washers, all that cr*p kills alternators a lot quicker than necessary. Be frugal, when you can.
I miss that 1987 Toyota 4x4 xtra cab, I could fix almost anything on it that wore out or needed replacing.
Get a factory rebuilt, if you won't do it yourself. Of course if they see you driving an expensive car, they are going to try to milk you for an expensive part.
8.5V on the battery, don't be surprised if you need a replacement battery soon too.
Dad still has his original 2000 Toyota Avalon. 73,000 miles on it. People bug him all the time asking him if he wants to sell it.