May be UK is especially cheap for car repair but costs you mention are unrealistic for major repairs on those components. I had gearbox problems on 10 year old car and independent mechanic suggested to sell car to scrap yard - in his opinion trying to fix it will end up costing more than car is worth. It was before Covid inflated used car prices though.

From quick check in google: If you are extremely lucky, you’ll get your transmission replacement completed for $2,500 all in. If yours is one of the more expensive types, it could easily range to $6,000 or even more.