Backless and low back wheelchairs are definitely a thing, though fortunately not for cost savings, but for better mobility for the user.

If you have really good T-spine mobility and control, it can sometimes be beneficial to get rid of the back of your chair, giving you more range to twist, turn, and lean from the hips.

With enough upper body strength, If you go for a lightweight no back chair with tip wheels, strap in, and get some durable gloves, you can even do full cartwheels in a wheelchair.

Obviously whether a backless chair is appropriate is very individual and a physiotherapist and occupational therapist will need to help assess.