I think it's good to have at least two pairs of good shorts, but yes it does get expensive to have more than that. I often handwash a pair in the sink if I don't want to do a full load of laundry.

As for bacterial stuff, well... I have a little bit of a theory on that which may sound a little kooky. As we all know, healthy woman should have a good flora balance which has beneficial bacteria that fight off bad bacteria and yeast. Well, I figure that my shorts probably have their own healthy flora culture that develops over time.

I never bleach or completely sanitize my shorts because residues from these cleansers invariably affects my own flora. So I just use a very mild unscented detergent and water to clean my shorts and rinse very well. If I'm fighting a yeast infection and have to ride, I'll use a bunch of miconazole cream on the chamois pad instead of just running dry or using the typical chamois butter.

Also, I often carry wet wipes on long rides to make sure that I've thoroughly wiped especially if I've had to go #2 - since I don't want any of that culture growing in my shorts!