I haven't found a whole lot on quite exactly are the SKoreans looking for. Are they just looking for reasonable upgrade/replacement of equipment than F15SE will be quite good, nothing drastically new, already F15K in service, should be no big surprise price wise. SK can go with Eurofighter also, very good technically, might be a bit pricey but they should get plenty of industrial work and exchanges of tech. And if Skorea gets India to pay for all the work on the new goodies, why not, let someone else develop it with their money and buy when it is ready.
I really don't see LO as being a major issue, how much is it really required when your main adversary is NKorea? Do you really want to spend billions more because...? The main Nkorean SAM is S125/S200, not exactly new or little understood by Western forces. You probably could buy some Growlers for a heck of a lot less than how much you would have to spend on LO technology acquisition and maintenance.
If PAKFA is an option, well, my guess is SK would only buy that if they feel China is a bigger threat down the road than NK. NK flies some old Mig21s and a few Mig29s and you really have to wonder how much flight time a NKorean pilot gets with the penury of gas in that country. I haven't heard of China donating J10s or J11s to NKorea so why would you buy such a massively superior fighter to what ever Nkorea is going to have? Considering the amount of business SKorea does now with China, Nkorea is almost more of a headache than an asset to China, again, notice how little military equipment has been sent to NK by China or Russia for that matter in the last couple of years. Speaking of Russia, if there is a chance of SK buying PAFKA, with REAL hard currency not whatever NKorea has, I think Russia will quickly forget Nkorea even exists.
F35 could be in play but when will it be available to Skorea? Again, it might be a bit too much technology for the mission. One thing though that could come in handy and I haven't seen LMT talk about this, which is strange in my opinion is SK actually could really use the F35B! Because of all the artillery Nkorea posses and well known location of all air bases in Skorea subject to all kinds of attacks, F35B actually makes a lot of sense in that theater. Also SK isn't the Middle East weather/heat wise so F35 won't have to battle extreme heat there and mission ranges should be quite acceptable. F35 is no Harrier (no taking off in the parking lot) but the fact is you should be able to deploy it at numerous locations around the country after the main runways are taken out. If LMT can come up with a decent package and availability, they should have a good shot at this one.