There aren't going to be any discounts during the peak summer months. We're going Friday-Monday for the second time this summer, and both times our room at Hotel Breakers (not to be confused with Breakers Express) has been over $200/night. However, the convenience is TOTALLY worth it. You can walk to the park, plus on-site guests get in one hour before opening.
All of the other hotels in Sandusky are pretty expensive ($100-150+ per night) and none of them are more than 2 star, not to mention you have to drive yourself to CP and pay to park.
If you can go in May or October, sometimes there are some Castaway Bay discounts, and Breakers Express is pretty cheap year round. But they don't put out any "codes" or anything like WDW does. Try going to the CP website and looking at their packages.