Affordable 500 series blank panels from Nekotronics that look good.
Plain old blank panels are boring so heres an interesting one.
Depicting a typical Japanese back street full of izakayas (居酒屋), tiny Japanese bars that seat 2-5 people. These places are amazing, if you ever get the chance to visit some do so.
Made from FR4 pcb material that are 1.6mm thick in Red finish. These are slightly thinner than normal panels but that keeps the cost down. Stack them if you must have full thickness.