You only need a few inexpensive ingredients to make your own DIY car upholstery cleaner and get the inside of your car looking like new again.
Those ingredients are: grated soap, Borax and boiling water (plus lavender essential oil, if you want a nicer smell). Stir everything in a bowl until it's foamy and the soap is dissolved and then scrub it into your upholstery.
As the photo above from One Good Thing By Jillee shows, it could be well worth the effort.
A Simple and Effective DIY Car Upholstery Cleaner [One Good Thing By Jillee]