When you get the quote for the repair, I would ask the garage to give the car a thorough inspection and tell you what shape the rest of it's in. Then you'll be in a more informed position to decide whether to proceed with it or not.
Personally if my car needed an engine repair or a transmission I don't think I'd even hesitate, lets say it needed a £3k repair, what the hell else am I going to buy for £3k that would be already exactly set up how I like it, well-maintained (by me), up to date on all maintenance etc.