I just attended a webinar, eBooks and Audiobooks for K-12 Schools, sponsored by OverDrive. Their School Download Library service was explained and demonstrated. The service includes eBooks, audiobooks, video, and music, though, you can select the type of content you want. Two models were explained: One student at a time (content purchased) or Unlimited, simultaneous use (content by subscription). Or a combination.
OverDrive customizes a remote website for your needs with selections from 300,000 titles with use options like burn-to-cd, print, read-out-loud, transfer to portable devices, and access from mobile devices. You can also upload your own content, anything that is available in a word document. Training is included as well as MARC records.
As for cost... the unlimited model is based upon student enrollment. The figure that was mentioned was up to 2,000 students, about $4,000/year. Sounds costly for a small school or district, however, about 50% of the subscription cost includes content credit to purchase titles and begin developing a digital collection. Other costs mentioned were about $10 for an ebook and $35 for audiobooks. I'm sure that cost for one time use would be much less and you can probably set up cost parameters.
I would recommend this webinar if you're interested in adding digital content to your collection. The webinar isn't archived, however, additional webinars will be offered in November. Check out the OverDrive website or schedule a private demo.