I would definitely not spend the extra to buy run flats. Just keep a tyre inflator in the boot, which in most cases will be enough to get home. Or, as you're so close, just walk home!
Personally, I'd go new, mid range. Kumho ps71s are really good value right now, or you could even get on tyrestreets and get some new accelera phis, would be fine for you I'd have thought, given that you haven't mentioned anything about a tyres performance, only it's price...
Edit to add, a full, 18" staggered set of 4 accelera phis, is just £176 with a 10% 'autoalex' discount.