I just noticed that the Tecarta Bible app has most of its study Bibles on sale for $4.99. You can see the list in the app or at the
Tecarta Bible website. Their Facebook page says it's a holiday sale that started just before Christmas, but there's no mention of when it will end.
Keep in mind that any study Bible comes with its associated Bible translation if you don't already have it. Once they're installed, you can use any translation with any set of study notes, so if a study Bible is offered in several different translations, pick the one you don't already have. For example, there are NIV, NKJV and NASB editions of the MacArthur Study Bible. If you already have the NKJV installed (or plan to buy the NKJV Study Bible), then buy either the NIV or NASB edition of MacArthur.