Alarm and Central Locking are not working

Good Morning, My Renault Clio 1999-2000 How much roughly it will cost to repair or replace.

- Initially the alarm started to go off without any reason even while driving.
- Someone told me to open all doors, when I did it stopped completely and never worked since.
- The central lock does not work. Checked the key but apparently the fault is not there.

I would like to know the repair cost to see if it is worth repairing them or buy another car (used).

Thank you.

Kacem