2 really inexpensive things you can do is paint and re-grout. You can do the job for around $100 and some elbow grease.
Check the color of the grout for yellowing. Also check for voids. If either is present, use a rubber grout trowel to force the new grout into the joints. Re-caulk the wall-tub joint.
After the grout and caulk are completely dry, apply a grout sealer to retard moisture and inhibit staining. Now, on to the paint.
The fun part of painting is selecting a color scheme. The rest is work. Work from top to bottom. Start by painting the ceiling to prevent any paint spatter. Finally, paint the window trim, door trim and baseboards.
If you can afford it, consider updating the shower curtain or shower door with a new model. Other nice touches if your budget allows are new mirrors, light fixtures, towel bars and faucet.
references: bill & kevin burnett, inman news, efrogpond inc, donsrealty.net