Sounds like you need to sell the car and buy another! Sell it to me and I will fix it myself using the info already given in this thread.
Or, continue to drive it if the fault has gone away. It ain’t going to leave you stranded.
Seriously, get another quote from a different garage. Sounds like your garage are trying to have your pants down. That quote is about twice what the car is worth!
Main dealer be quote for a brand new column fitted
As others have said you get get a refurbished one for a few £100 and likely about the same again for fitting from a independent