I would run the Kent until it fails, see how long it lasts. The Sun Bikes appear to be steel, which will rust out in a salt environment too. I have a pair of Huffy cruisers that I bought used that we keep at a beach house at the NC coast. The main upgrade I did to them was a stainless steel chain. I hose them off a few times a season and keep things oiled up. So far they have lasted 5 years, most of the bolts have surface rust on them.
Aaron