What shape are they in? What are they made of? A photo would help
Need more info and pics please.
“Cheap” and “shower walls”, may be a “challenge”.
No other area in the house needs to be more cleanable and more water proof.
If you’ve water damage or mold now, that must be addressed now. Then one can go on from there.
Use self adhesive stick on tile covers?
That is not an area yo skimp on. Need to keep it eater proof whatever you do. Baths are not a cheap fix.