I had same problem before.
My diagnosis for your problem is that the surroundings (boundary between the wall tiling and the shower pan is leaking because of the aging of the grout. Rarely, the middle of shower pan (even it is tile glued together in stead of a one-piece pan) leaks. It has water-proof backing.
Method to fix: 1) dig out the aging grout between the wall tiling and shower pan; 2) seal the space with alphalt (may not be essential); seal the space with sanded grout; 4) glue 3’’ small tiles (L shape) above the sealed crack. Done!!
Let your contractor do this. 32K to replace it is ridiculous. Doing things which is not necessary is the way contractor to make money out of you!!!
Good luck!