I bought two used hand brake mechs. One from a great guy on this forum and another from a breaker on FB.
Didn't want to risk it so compared the two and used the best one. Actually both were pretty much equally in good condition. They did have slightly different springs despite both coming from E85s. One looked newer. Might sell the unused one or keep for rainy day as unit is on back order.
One was £120 the other £150. (New, £400).
Total repair bill including the parking sensor thingy, labour etc, was £250. So, around 400 all in if I sell the surplus unit.
The teeth on mine were gone in the middle, sounds like you have worn unit too. Can lead to an MOT failure.
Low milage car. Previous owner must have rode the ratchet every time he used the HB. Always depress the button to save this known weakness of the Z4.