If you expect to live there another 20 years, then kludging this ought to be off of your radar. If you want to turn this into an actual tub/shower that for sure won't have water damage, then you need to save your pennies to do the reno right.

In the meantime, for the next few years while you do that saving, if you are fearful of the potential for water damage, as you ought to be, covering the walls with something like FRP would work better than paint. You can find it at the local box stores, and although not pretty, if you keep the corner seam caulked, it will be waterproof until you can rip everything out and start over with a correctly built tub/shower area.

Then you can use any semi gloss paint outside the wet area. And either run the vent fan or open a window after use to keep things well dried out. Moisture is the enemy of all homes.

Waterproof paint cannot replace your shower curtain. You must keep the walls dry and then let the room dry out, as well.

Hollysprings urges you to save up for a real shower alcove installation. I understand that your finances are limited. I wonder if there are any church groups or grant programs for keeping seniors in their homes that could assist you with your project.

Those are really common sense answers that don't really address the actual question...

Obviously getting a nice one piece surround would be ideal, or having the entire walls demo'd out and done with fresh tile and proper waterproofing, etc. But can't there be a possibility of a good product to use? Yes absolutely, but what are they is the question.

Unfortunately, I don't have a great answer for you either, but I'm looking into it. I'm trying to find something that can go right over the tile too though, for you, just a paint / epoxy might work fine. I want something that can also be flexible enough to span cracks, but your application just going over regular walls down to the tile may not need that exactly. I haven't tried the Zinsser watertite clear but I've been looking into it, which is how I came across this, hoping to find some clues for my own. They have a clear that might work just fine for you, not sure if you used like the white for example and didn't know there was a clear. You would think someone would have a decently abrasion resistant, clear, semi-flexible coating that goes on like paint for tiled showers to seal them and make a million bucks, I'm honestly quite surprised it doesn't seem to specifically exist.

For your application just about any marine clear epoxy might work too, followed by a good uv coating since you probably don't have to worry as much about cracks as I do. FlexEase was one I found that looked good.

*I realize this is an old question but thought there is a possibility you might still be looking for something, or if you found a good solution, please let me know what your experience was with it.

I am looking for the same thing so it is still relevant

Everyone wants a hack shortcut and can pay to repair the damage it costs, but not to do it right the first time.

"Plasti Dip is a multi-purpose, air dry, speciality rubber coating. Available for purchase in easy to use aerosol cans, it is ideal for wheels and small automotive refinishing applications. Use it to change the color of your wheels, emblems, trim, mirrors and more! Plasti Dip Spray is easily reversible when you decide you want a new color."

Hey, if you can Plasti-Dip you car, can you Dip your shower, as well? New Product Combines Pearls and Topcoat with Plasti-Dip Color Coat

And you don't use aerosol cans for large projects, you use a paint sprayer.

Yes, you need a respirator, so maybe you have to move out for a day or more, and you can't use it in a multi-family building. But they show it being used with a pressure washer, so as long as you don't have a peeling edge, you should be fine to shower with it. Plasti Dip is famous for being able to peel right off when you are tired of the color.

Someone should check into it. The new product comes in 24 colors.