Unless your bath tub is badly rusted or pitted, painting it yourself may be easier than you think. While you'll need to use epoxy enamel paint for the inside of the tub (available in kits, making it easy to apply), you can use water-based enamel for the outside. Paint the inside fresh epoxy white, then paint the outside to match your bathroom decor; or get creative and paint stripes, leopard spots or whatever else you fancy.
Clean the bath tub, inside and out, using muriatic acid or another chemical cleaner. Purchase the epoxy paint first. Some kits include a cleaner.
Sand the tub. Use an electric palm sander and 80-grit sandpaper. Sand thoroughly until the surface is completely dull. You are not sanding to remove paint, but to make it rough so subsequent coats of paint will adhere.
Remove the faucet and drain insert. If this isn't possible, carefully cover the fixtures with masking tape. Use a plastic bag, secured with tape, over the faucet. If you're going to spray with epoxy, mask all the adjacent areas to the tub with at least 2 feet of masking paper or plastic.
Apply the epoxy bonding agent with a lint-free rag, cheesecloth or a spray bottle. Allow it to work for the recommended time, usually 5 minutes. Only apply the bonding agent to the portions of the tub you'll be painting with epoxy. If you're planning to use a different paint for the outside of the tub, leave that portion for last.
Mix the epoxy according to directions. Most epoxy paints are in two parts (the coloured resin and the hardener) and are mixed right before application in a clean plastic bucket.
Apply the epoxy with either a paint sprayer or good quality synthetic paint brush. Paint two or three coats of the epoxy.
Clear-coat the epoxy with the acrylic finish coat, using the same method used to apply the epoxy. Follow product directions. Typically you should apply at least two coats of clear acrylic, waiting 30 to 60 minutes between coats.
Prime the outside of the bath tub with bonding primer, and paint it with high quality latex enamel. Choose a colour that matches or complements your bathroom, or consider a decorative or faux finish.
Look for a bath tub painting kit, which should contain the cleaner, bonding agent, epoxy and clear acrylic top coat. Most hardware and home stores carry these kits. A sprayer will give you a smoother epoxy finish than a brush.
You may need to wait several days before using the tub after refinishing. Read the directions and plan accordingly.