Had a bad experience with Avis Thailand in the past. They told all the fairy tales that they could invent not to return the deposit (they implied I smoked in the car and I'm not a smoker, then 'you had accident' ect ect). Never again. Hertz, Sixt and Budget much better.
However there's always a lack of available cars during Xmas, not so easy to find something available at the moment
If that includes Super Collision Damage Waiver the price sounds about fair. Also the daily rental rate is likely to decrease if you book for at least 30 days
Overstayed by how many days? Are you in Thailand now or abroad? Have you been blacklisted or did you make away with a fine and an overstay stamp? You are providing so many details that's so easy to understand. Try being more terse 🙋♀️