I used to work for a major window company and yep, a lot of big windows and 4 sliding doors (how big is this house?) are going to be expensive.
If cost rather than a lot of hand holding is important, going through a big box store will save you money as compared to going to a dedicated window store for that brand (even with my employee discount it was usually cheaper to buy windows through the big box store).
Also, a lot of the cost adders (at least for the company I worked for) once you had picked the basic material of the window (i.e. vinyl vs. wood) and its size were for decorative things. For example, the basic wood window vs. the fancy wood window had all the same quality of materials for wood, glass, etc. So go for the standard options for window color, hardware finish, etc. rather than the special upgrade ones.
I will also add one you get past a certain point (and I've run the numbers) additional coatings, etc. to get a better U-factor and Solar Heat Gain Coefficient (and exactly what levels you'll want depend on your climate) will save you minimally in energy costs vs. the extra cost of the window. But given that the windows are from 1969 and you have holes in them :-) you should see improvement from a basic dual-pane insulated glass window.
So I would say wait for a sale and replace the windows a couple at a time, especially since you say a lot of them aren't urgent to do.