Jean, regarding Mixbook, I usually wait until a 55% discount with free shipping offer comes around. It seems there's a different sale every few days, and it's worth it to wait. Not all sales apply to all variations. With Mixbook, the 12x12 inch layflat books get a bit expensive if you order the thicker pages, that are almost like cardboard. The first time I ordered these by accident, but I have since decided I like the heavier weight. One really needs to read the details about the page options- I missed that the first few times. I have only made the 12 x 12 inch books, so I don't know if the other book sizes offer a choice of paper thickness. I also like the matte finishes best.
The Mixbook results are very high quality , and I'm very happy with the finished product. With each book I make, I've learn more tricks, and the Chat Customer service is really helpful. I have learned how to save favorite backgrounds and stickers (click the heart in upper right corner of the choice.)
It's late here, tomorrow I'll check prices I've paid, page totals, add more details regarding the different paper weights.
I haven't found any place that is priced the same as the Costco photo books were , and I could never get Costco to tell me who their photo vendor was.