As far as libraries and budgets go. I can't see how new formats has to cost libraries or anyone for that matter more.
As consumers, we have to pay for our books at prices on the range of $2 to $10 or even more per book, even in ebooks. However, we have to realize that unlike DTBs, our books don't really have a manufacturing cost (i.e. the actual commodity portions, not publishing, authors, etc). I have no problem with the consumer market, but the reality is that if Overdrive or anyone wanted to make books available in a Mobi format, it doesn't have to cost anything to make all those epub books available in mobi. It doesn't mean it won't cost, but it really can be just as simple as converting a file from Epub to Mobi... i.e. disk space.
That being said, I realize that the cost to libraries seems to be more related to each time a book is borrowed or some type of model like that, but I can't say whether that is good or bad without knowing how libraries operate with regards to DTBs.
Given that Libraries in general tend to be financially strapped in our current economy, and I can't help but feel that there will be some benefits to Ebooks in the library.
1) It will make libraries accessible to many working people who are restricted due to lost library hours
2) It may make more libraries accessible to people. I've seen that in California, I can take advantage of the LA or SF public libraries that are normally out of my reach.
3) It may make people more interested in supporting their public libraries.
4) It may save money for libraries who can shift their policies to work with the ebook system and not against it.
It could also cause more harm than good, but we won't really know until it happens. The conservatism in this world with regards to digital formats in the consumer industry seems to hurt most when the business models would rather stick with the status quo (Music, Books, Etc). We must face it, Digital formats are here and we should learn to incorporate them in all aspects of business be it libraries or the publishers.
---Sorry if I digressed too much.