I used a product made by a company called Transolid. (Imo, stay away from acrylic) http://transolid.com/transolid-shower-walls I purchased the shower base from them as well. Shower door came from Lowes. I would definitely recommend the product. It's a composite material and little difficult to work with but the shower turned out unbelievable. I used a jig saw and a belt sander to get the panels to fit perfectly. You can get full wall height size panels (92 inches in my casel) and I used PVC tounge and groove panels for the ceiling. More on reddit.com

I see a lot of these installations in hotels, and I've installed a few of them for myself over the years. It's much less expensive to install than tile and, as you noted, easier to clean. If the appearance is ok with you, go for it. I think Onyx makes quality products. https://www.onyxcollection.com/shower-wall-panels.html More on reddit.com

Use the cheap fibreglass until you can afford tile More on reddit.com

There is usually a version sold at big box stores. You can akso check tile stores. I have done 3 showers now with Onyx. The best advice for installation is to make templates. I rip down 1-1/2" wide strips of 1/4" plywood, and make some 6" squares of the same plywood. Cut down the strips and scribe them as necessary. I nail the strips together with plywood gussets, CA glue, and my 23 ga pin nailer, so that they form the exact layout of the wall. I use the 6" squares with proper sized holes cut in them to locate things like tub spouts, shower valves and shower arms. Once you have the templates built, pull them off the wall and lay them on top of the panels to make your cuts. The panels can be pretty pricey, and the templates basically guarantee mistake free cuts as well as a quality install. More on reddit.com