I've seen a couple of stunning X358's going, one was £17k, 4.2Ltr 75k miles, the other two in the £11k to £13k range. No idea if they are taking the proverbial or if that is a fair price range for those cars?Hope you find the fix and get her sorted for much cheapness LG then decide from there.
Seems like you may stick with the brand after all, maybe an XJ X350 / 358 would be a good call.
Or......There are some high mileage, but very good examples of XJ X351's out there. I know of one for example that will be going shortly, albeit at high mileage, but with a ton of money spent on her and well looked after, for not a lot of money.