With space becoming more of a problem nowadays nobody has the space to have a really large bathroom, especially if they live in a crowded city. This being the case efficiency in 
space utilization is what is most important.
Most people therefore do not have a separate bathroom mirror and a separate medicine cabinet. They both are merged together as bathroom medicine cabinets with mirrors. In fact with the number of different models that come nowadays these actually look better than getting a traditional mirror.
Take for instance the recessed medicine cabinet. For all purposes and intents, it is just a mirror until you open it and it forms the medicine cabinet inside. You also get the large paneled ones for those who want more storage space. You can pretty much install however many panels you need in your bathroom and each of them come individually as a cabinet with a mirror on the front.
If you have the space, you can actually install a small cabinet on either side of a large mirror, giving you a paneled mirror. Of course the disadvantage of these paneled ones is that you cannot have the lights on the side of the mirror and will have to have one over the mirror.
Of course if you go a little higher in the expense scale, you will find bathroom medicine cabinets with mirrors and lights. These lights come as attached fittings on the cabinet itself so that there is no extra installation required other than that you plug it into an electricity source.
If you are really that particular you can even get full length cabinets with a mirror so that you will have a full length mirror in your bathroom. Some of them are actually quite substantial things and can even be used to store stuff like towels and are not only medicine cabinets.
Obviously these are very expensive and can cost nearly $400. In bathroom mirrors, the price depends on the brand and the very same thing from a lesser known brand can cost considerably lesser. Going online to check is therefore a good idea, and you can even avail of a lot of discounts if you purchase on the net. Make sure that you read the fine print about return policies though, unless you want to be stuck with a cabinet with a broken mirror.