I'm guessing you are located in NSW, given your experience with the Roads and Maritime Services (RMS). Car modifications can certainly be expensive! There may be funding assistance available through the National Disability Insurance Scheme (NDIS) or the Synapse brokerage program.
I would encourage you to speak to an occupational therapist (OT) who is specialised in car modification and driving assessments. The OT Australia website has a directory which will be useful for finding an occupational therapist whose area of expertise is driving - https://www.otaus.com.au/find-an-occupational-therapist
The following links contain further information about the NDIS and Synapse program.
NDIS - http://ndis.nsw.gov.au/ready-for-ndis/
If you'd like to speak with one of our health professionals over the phone, you can call us on StrokeLine (phone 1800 787 653, Mon-Fri 9am-5pm AEST).
Best wishes,
Kirsty (StrokeLine)