You seem to be suggesting that cost should be a deciding factor in whether to protect creative work.I suppose I am, but only indirectly.
I view both copyright and patents as economic instruments. To me, the argument for temporarily restricting freedom to replicate others' work is based on the "greater good" that comes from incentivizing the creation of that work in the first place. However, that argument only makes sense where such an incentive is actually necessary, and to the extent that it is necessary.
If something really can be created by someone within a weekend, it is unlikely that the work or insights necessary to create it are particularly unique or valuable. There is little need to incentivize creating or sharing such work with years of exclusive control, because probably many others could (and some will) do the same thing anyway within that time, and granting the exclusivity is just an artificial barrier to any greater progress that any of those creators might then make.
On the other hand, maybe identifying a new antibiotic that will save thousands of people from "superbugs" takes several years of expensive laboratory research and then several more years of expensive trials and regulatory approvals, but once identified the marginal cost of manufacture is relatively low and many organisations have the resources to produce the physical product. It seems quite plausible that the research and trials and approvals won't happen in this case unless there is some extra benefit to whoever actually puts in the time and resources to do that work first. Given the likely benefit to society of having access to new antibiotics, I personally don't have a problem with incentivization in this case. (For the same ethical reasons, I also don't have a problem with revoking any exclusivity if whoever holds the rights isn't taking reasonable steps to use them by producing and selling the drug at a fair price; the goal is to promote discovery and availability of a useful drug to those who have a medical need for it, and anyone who isn't actually contributing to that doesn't need special privileges.)
Perhaps it would be more accurate to say that I think the cost/benefit should be a deciding factor in which classes of creative work receive these kinds of protections. It's not so much about the absolute cost, but rather whether it's worthwhile for creators to create already, and if not, whether the value to society of having the creation available justifies offering some extra incentive.