dimensions.txt

Here's some dimensions of popular programming books on Amazon:

minecraft for dummies 5.4 x  8.6 x 0.3 inches
touch develop         6   x  9   x 0.6 inches
don't make me think   7   x  9.1 x 0.5 inches
learning python       7.1 x  9.3 x 2.8 inches
beginning c++         7.2 x  9   x 1.1 inches
node.js in action     7.4 x  9.2 x 0.8 inches
unity 4 by example    7.5 x  9.2 x 1.2 inches
html & css            7.9 x  9.6 x 1   inches
invent your own games 8   x 10   x 0.9 inches

Print on demand printers:

lulu.com
createspace.com
lightningsource.com
blurb.com (seems to target mostly photo books)
bookbaby.com

Based on those and looking at prices on Lulu, I think the best choice is:

Product Line: Standard
Binding: Perfect Bound Paperback
Product Size: Crown Quarto (7.44 x 9.68 inch)
Interior Color: Black & White
Paper Quality: 60#
Cover Finish: Gloss
Cost per 280 page book: $9.80

On CreateSpace:

Interior Type: Black and White
Trim Size: 7.5" x 9.25"
Number of Pages: 280
Quantity: 1
Per Book: $4.21 each


Margins:

InDesign Classroom in a Book:
  Bottom: ~0.375"
  Outside: ~0.375"
  Top: ~0.5"
  Inside: ~0.875."

SICP:
  Top: ~0.5"
  Outside: ~0.75"
  Bottom: ~0.75"
  Inside: ~1.0"