A 2007 Hyundai U1 diesel is a sound engine but few have yet covered really high mileages and other parts such as clutch , gearbox and suspension seem to have more issues than the Skoda's that I have owned and driven .
The I30 1.6 L diesel is cam chain rather than belt so no worries there . All models seem to suffer from suspension part failures , these though should have addressed under warranty . This forum is worth a look for prospective I30 owners :-
http://www.i30ownersclub.com/forum/
I have a I30 myself , a 2010 1.4l petrol , not sure if I would touch an example with that high a mileage . Guess it depends on how much you are looking to pay though .
If you are doing 7-10k year a diesel would only save you £180-£250 in fuel pa but repairs to a diesel motor can be expensive .