I have a K-S2, I started reading about the aperture failure problem after buying it and got worried for a while, however, in this forum there have been only one or two reported incidences. If you live in the US, the repair cost is not exorbitant, or you could do it yourself, there is a thread here saying how to fix the solenoid that causes the aperture failure.
After comparing the the K-S2 and the 80D in
this site I think the K-S2 is better value for money, but they are cameras in different ranges. The 80D compares with the K-3.
If you want to stay with Pentax (please do!) but don't want to risk that aperture problem, try looking at an used K-5II, just recently there was one in the marketplace here that included two kit lenses (18-55 and 50-200) for just 50 usd more than the offer you found for the K-S2.
Anyway, I can totally recommend the K-S2, if the offer is a colored version, even better, those colors make the camera even more unique.