I am pursuing a teaching post in the UAE. However, my mum lives with me and I need to take her with me. I have been told that she can enter on a 90-day visa but will have to keeping renewing it. How much does that cost each time?
To be clear - there is no such thing as renewing a temporary visitor visa.
All temporary visit visit visas can be extended for a period of 30 days for 570 AED; you must extend the visa before the expiry date.
However once the extension expires, you must exit and enter on a fresh visa, and the cost is the same as applying for the first time.
Once your permanent residency paperwork is completed, you can then sponsor your mom to visit you under a visit visa.
If you want to bring your mom with you when you first arrive, she will have to come under a tourist visa - which you can get from any hotel or airline. These however are of limited periods and not extendable.
Once the tourist visa expires, your mom must exit and you can then recall her with a visit visa.