It is illegal for a landlord to discriminate as related to a persons disability, the Americans with Disabilities Act, ADA, requires that you make reasonable accommodation for people with disabilities.  The operative word is "REASONABLE" you are not required to make unreasonable accommodation by making expensive modifications to the rental unit.

A landlord must allow a tenant with a disability to make reasonable modifications to the rental unit to the extent necessary to allow the tenant “full enjoyment of the premises. The tenant must pay for the modifications. As a condition of making the modifications, the landlord may require the tenant to enter into an agreement to restore the interior of the rental unit to its previous condition at the end of the tenancy. The landlord cannot require an additional security deposit in this situation. However, the landlord and tenant may agree, as part of the tenant’s agreement to restore the rental unit, that the tenant will pay a “reasonable estimate” of the restoration cost into an escrow account.