Since he is alone I would head right out and buy a product like quick cure. It normally isn't a great idea for bigger tanks as it can contain copper which will kill bacterial filters and inverts like snails and shrimp. But for just the betta it is probably a good idea.
Also, if I were you I would do at least a twice a week tank cleaning of upwards of 50%. It isn't a lot of water, doesn't take a lot fo
time and will make the Bettas environment so much better. You mentioned that the water was yucky last time you changed it. Well it shouldn't ever get to that point. It is easy to sneak up on us though, so jumping in premptively is always a good idea.
Follow the directions exactly on the meds and everything should clear up hopefully. Also don't forget to keep up the medication for up to 4 weeks after the last signs of the ich. The salty bits you see are only the final sign. It has a life cycle and you must wait until the last bits have hatched and are killed by the meds.