Keep plumbing where it is. It costs on average about 5 thousand dollars each time you move plumbing fixtures. So work with your contractor on a plan that keeps all your existing piping in place. This alone will save you a lot of money.
An easy DIY Fix for a bathroom is to ad a frame around your existing builder grade mirror. It will not only look great but also hide any age related wear against the edges.
You can make a drastic change to your bathroom with a little lighting change. Change those builder grade lighting to something brighter or unique can be an easy and relatively inexpensive task. Adding lots of light to a bathroom can also be a very valuable change to a homeowner. Save money by shopping sales on lighting and not being in a hurry. You may also want to consider adding a skylight tube or larger window to your bathroom to bring in more natural light.
Of course the biggest change most people want and need is their actual bath/shower area changed. This can make the most drastic difference in your bathroom. Some people shy away because of how much people think it would cost to change. If this is you their is a much more affordable solution. You can have your Bath tube or shower refaced or even convert your Bath tube into a shower.