I refinished a tub several years ago, using a two-part epoxy kit.
I loved the look of the final product, and the total cost (tools + materials) was about $75. It took about 3 intense days.
Surface prep is critical. You cannot clean it too much! The epoxy will not adhere to impurities, leading to bubbles and peeling at the site.
It stinks! You need excellent ventilation and a respirator. Sensitive people may need to move out temporarily.
Apply in multiple thin coats. Put the epoxy in the freezer between coats, so it doesn't dry up. I was able to put on one coat more than the package recommended, which I think helped.
It lasted fine for two years, in a house with 7 people and two bathrooms. Then we moved. My sister used the same kit, in a house with 4 people and one bathroom, and had a bit of peeling around the drain after a few years. That was remedied with touch-up paint.