If a song costs $0.99 with DRM then it would cost more without DRM. Very simple. In most cases the DRM terms of use are acceptable to me, which is why I don't hesitate to buy DRM'ed content.
Of course, many DRM implementations are highly annoying, but that is a design issue not a core issue with DRM technology.
In the vast majority of cases, DRM is only an annoyance. It doesn't stop anybody who really wants to share content from sharing it. The only things DRM does is give undue power to content sellers (like Amazon) and make content completely worthless when whatever technology is used to verify ownership stops working (or gets turned off like MSN Music, Yahoo Music...)
Why shouldn't I be able to plug my iPod into someone else's computer, pick the songs I want, and confirm a popup for the amount I'll be billed? Or why shouldn't it let me listen to the songs for a few days free of charge?
DRM should let comtent owners think of extremely creative ways to virally market digital goods, while still preserving ownership and the ability to make a profit.
Sadly, there has not been a good DRM yet. Even Apple's DRM is so stupid that if you get a hard drive failure you can't re-download the songs free of charge (or for the price of bandwidth). I happen to have had two hard drive failures, and only the first one was covered. This is bad business, not bad technology.
Since when does price have to do with how much something cost to build? If I spend $10 building a shitty chair, it's still a shitty chair. DRM-protected music costs less because you're buying the right to listen to a song with restrictions not present in non-DRM-protected music.
It seems that RIAA and MPAA are the luckiest of these middle men and the most persistent, and that is why they came to make such a huge profit from what was relatively obscure nook of an intellectual property regulation. After all, the concept of an artist having the privileged right to his, already published, work comes first, and all the delegations and copyright issues come second.
DRM is designed to keep power in the hands of rights holder, the creator, and, by necessity, away from the consumer, and only the monstrous bulk of MPAA allowed them to effectively pretend that they are not the simple middle men, but the focus and origin of all the rights that anybody can ever have on IP.
DRM is the sort of technology that could enable this kind of free, expressive creation. That we don't have it is a failure of businesses to come up with creative licensing terms, not a failure of DRM technology.
So while "buy" isn't the right word, neither is "lease". It's a whole different beast altogether.
You can buy a car but you can't drive it 100 miles per hour. You can buy 1000 smoke detectors, but you can't harvest the radioactive isotope and make a nuclear reactor. You can buy a book on paper, but you can't re-publish it as your own work, etc.