1. Yes, it can be manually adjusted. If you turn it on using the right button, it's in manual mode. Using the left button is auto mode. But as soon as you mess with the brightness settings in auto mode, it reverts to manual.
2. Airsoftparts.ca carry Hurricane sights. Only one they have listed on the site right now is the 553 and it's out of stock. Their price is $239. But like I said, watch the classifieds. They regularly appear for $200 or less.