In the dining room I would say you might call a window company to make custom thermal broken windows for the sizes you have. They'll be able to install them in the existing openings in most cases if they're not opening windows. And that is replacing glass, rather than whole windows, so it would be lots cheaper.
If you can buy a standard size to fit your opening windows, I'd recommend going to each of the big box stores in your areas, seeing the brands, and then look for reviews. Usually, if you buy them at the store, their installation is a lot cheaper, too, if you aren't going to do it yourself.