These have been on sale before, but not this cheap.
The NKJV Study Bible: Full-Color Edition is $2.99. As I mentioned before, the paper version is quite spectacular, but the ebook version is nearly the same as the original
NKJV Study Bible, but with some pictures thrown in.
B&N
Kobo
Amazon
NIV First-Century Study Bible: Explore Scripture in Its Jewish and Early Christian Context by Kent Dobson is $2.99.
B&N
Kobo
Amazon
There are actually quite a few study and devotional Bibles on sale right now for $2.99 and $3.99. Here's a link to
Christianbook that lists the ebooks on sale that are also Bibles.