If your overbite is that extensive Invisalign might not be the best option. It would only be able to decrease the overbite slightly so it really depends on what your end goal is. They would also have to evaluate if tooth extraction is an option to fully correct the overbite.
You can certainly get your cavities filled while you are in aligners. Given this situation, I normally fill one or two cavities at a time to make sure aligners still fit properly afterwards rather than filling them all at once.
If they weren't included in your treatment then you can expect to pay $500-$750 in most areas. $1100 does seem a little high.
You can go to any Invisalign dentist to get Vivera retainers.
