To print your book commercially you will need to reproduce the color faithfully and with all bitmap elements at 300dpi.
Frankly that is difficult to do from Pages which is designed to print to a users' desktop printers and renders certain parts of the output at 72dpi when exported to pdf which is the usual format for commercial printers.
1. See if you can find a commercial printer who will accept a Pages file to run through their RIP directly
2. Always talk to your printer about what they require and what is achievable
3. Commercial offset works off a different price structure than digital printing. Much of the cost is up front and the greater the print run the more the price comes down. Find out how many books you'll have to print before you beat the $8 you have been quoted by blurb.
4. As compensation commercial offset, when done correctly, is markedly better quality than digital
5. Please please please don't use Photoshop Elements or Photoshop they are not DTP software and rendering all your vector objects and text as bitmaps is such a bad idea that of course everyone is doing it now