The catalog (and site) lists every single book used in the core. Each book is available to purchase individually so they are listed individually. So you could easily use it as a book list.
We bought the book of time but didn't use it. We aren't into timelines I guess.
I feel that is a place I would personally cut back to save money. If your family adores timelines it might be worth it to get.
I recommend looking at the IG samples on the Sonlight site.http://www.sonlight.com/samples-sonlight.html
You might also find this site
The core IG includes the schedule pages (4 -day on one side, 5-day on reverse side no matter which you buy), suggested learning objectives in the study guide, maps, discussion questions and vocab development for read alouds. No tests or worksheets. The readers IG includes weekly schedule sheets with discussion questions and sometimes references to maps. No tests, worksheets, or crafts.
I didn't really rely on the discussion questions from Sonlight. I found that questions suggested themselves as we read. If you don't need a schedule or suggested discussion questions then you probably could do fine without the IG. There are several sites with hands-on-activities to supplement Sonlight if you want that and you might find free discussion questions for some of the books.
The LA IG includes the schedule. There is a spelling word list, a student activity sheet, writing assignments, assignments for Explode the Code and Wordly Wise (both optional) each week. You are supposed to do a spelling pre-test and test each week. The LA schedule lists the readers for that week as well.
I felt the LA was complete but my dd didn't respond well to the structure of it so we are going to try something else.
I have not used the Sonlight science. We just got a book of experiments on sale and have used other low cost or free resources for now. We did get The Living World Encyclopedia and Usborne Book of Knowledge and dd has enjoyed those. As dd gets older we might buy the science IG.
You should read the reasons not to buy Sonlight and reasons to try Sonlight-http://www.sonlight.com/not-to-buy.htmlhttp://www.sonlight.com/to-buy.html
I think they are pretty honest about what their curriculum is and isn't.
Ambleside Online uses some of the same books that Sonlight uses- not all in the same level though. They probably have a similar feel. Their history seems to go in a different focus though so you might look to see which you feel more comfortable with.