I think most of the books can be purchased in E-Book format, for example:
The E-Book does cost as much as the printed version however. You may also want to take a look at http://wrox.books24x7.com/
which is the online Wrox Library and allows you to view all of the books on there in their entirity for 50USD per 3 months.
Read this if you want to know how to get a correct reply for your question:
.: Wrox Technical Editor :.
Wrox Books 24 x 7