They can charge fees that recoup their costs and include a bit of profit. This doesn't work well. Folks aren't accustomed to paying for information online and will go to great lengths to avoid it. They can sell the print version and make the online one available to print subscribers only. This annoys the cheapskates but actually makes money.
Subscribers think they are pretty special.
They can sell the print version and post only a portion of its contents online. They can sell the print version and post the contents after the next issue is released. Both guests and subscribers will appreciate this. It's a tough business with all kinds of ways to alienate existing and potential customers. Trying to figure on fees is also a headache.