Exhaust valve

I would not just do the vale on that cylinder, the all valves should be checked and re seated as required. Also a crack check and re surface. The problem with this is that the engine may start to burn oil as cylinder pressures will increase and this can show up weak rings, it is a bit of a vicious circle. I would think that the miles you have done, the bottom end should be fine and a top end overhaul should not be a problem. I will ask one question, has the engine been using oil between services? If so this will probably increase with a top end overhaul, and if no, it should be fine.

Well its really what you are comfortable with spending. If the engine is using oil now, it will require a full re build or a second hand engine, both options will be expensive but so will be replacing the car, you best get a quote on the engine work and weigh that up against getting a new car, unfortunately its all about fiances and what you are comfortable with, if your car apart from the engine is sound and you have had no other problems, a replacement engine may be a better option, unless you buy a new car, a second hand one can be a gamble, you may just be buying someone elses headache.