Interactivity & output to iPad — epub beginner query

I have a very specific type of publication I want to format. They are ‘how to’ types of booklets (an ongoing series of 10 right now, and more in the pipeline), each with 12 pages or so. I’ve designed them in InDesign with a lot of interactive content which works just fine when output to pdfs. The main types of interactive content are:

• clickable on/off highlights, both for text blocks and for diagram images (this is the most important feature, because the content is complex and the user needs to be able to mark what they’ve done so far)

• pop-up diagrams and schematics showing greater detail/information

• outside linking to paid sponsors websites

• forward/backward buttons

• web style navigation bar

I want to publish these so they are viewable AND interactive on an ipad. Do I need to go the Adobe DPS route to do this or can I do this with inDesign? DPS is not an affordable option for an independent designer, as far as I can tell.

Other concerns; I think they need to be fixed layout, at least on the schematic pages.

Should I be looking at Apple’s IBooks Author or other software? (seems somewhat limited). These will be free publications of my own work that I’m planning to monetize in different ways, so they have to be very inexpensive to publish. I have read that Apple charges $350 or so to publish as an app, but nothing to publish as an ibook; is this correct?

I’ve worked in InDesign for many years, but I’m just learning the digital publishing side of things.

THANKS IN ADVANCE

Ellen