I'm a den leader in my 5th year, and I have leaned on my scrapbooking experience to get me through it more than I can tell you!
Do you have any idea if your classes are for every level of cub/boy scouting? There are some specific requirements that include creating scrapbooks but they're definitely not applicable to every rank. I'm imagining that your class is supposed to teach the leaders how to lead their scouts through a project, is that right? To that end, while the domino idea is totally cool and I think they would love it, I might try to identify a project that has more universally accessible/attainable tool requirements-it might be beyond many of the leaders' scope to drill into dominoes. Hard as it may be (and I mean that genuinely, it would be very hard for me!), I would try to rely on your "hard-core" scrapping supplies as little as possible. Of course they'd make a great title if you cut the letters out for them on your die cutting machine, but when they go to replicate the project for their den, unless they also have a die-cutter they would have to invest in letter stickers-that alone could break the budget. For titles, for example, choose a cool font and print it on cardstock and trim it down, add a trimmed cardstock mat to the kit. This is attainable for den leaders with any level of crafting skill. You could even provide the participants with a sample list of the fonts you use, and maybe a few tips on how to create word art, text boxes with borders, lined journal spots, etc... in a universally accessible program with MS Word.
Also, while you have lots of stickers to offer, they might not have that at home and would have to buy a lot in order to create a book with similar embellishments. Consider using some clip art that you hand-cut - while I realize that's tedious, it's also free! I've done that a few times myself, despite my ridiculous stash and my propensity to shop for supplies... when you have 10 boys doing 8 pages with 8 different subjects, it's just not possible to supply that many stickers (keep in mind, it's probably wise for each boy to have identical kits, especially at the younger ranks, so no one gets upset that Bobby got the better stickers, etc... that means cutting up one themed sticker sheet might not work if the stickers aren't all pretty equal in size).
Stamps are expensive as well. If you can find a way to create some cool stamps cheaply, with foam or whatnot, or find some dollar stamps that might be readily available at common stores, stamping is an awesome way to get embellishments while saving the money stickers would cost. You can include instructions on how to make their own stamps with the class materials, too.
As far as other embellishments, try to choose things that can be attached with glue sticks, because each kid in the den isn't going to have a Tombow (a first world tragedy, if you ask me LOL). I think it's a good idea to maybe introduce glue dots and pop dots in a select few ways to expand their horizons, as some leaders won't even know these things exist (or how utterly awesome they are!), but include the cost so they can figure that into their plans.
I might try to approach the project with the idea that the leader could conduct the project for a den of 10, for $20-$25 or less. Some packs have families pay weekly dues to cover supplies, some just ask families to pitch in their share for outings and project kits, some are totally out-of-pocket for the leader. I would even provide the participants with a list of supplies and cost to make 10 of the project, to help guide them in process of planning their own project.
The paper bag album idea I think is spot on! It teaches re-purposing (although they'll probably buy a pack of lunch bags
still more green than buying a Pioneer scrapbook or plastic binder!) as well as the creative stuff! You can probably appeal to wide range of ranks by focusing the page/subject organization one of three ways:
1) common activities by month or season: hiking and camping and Halloween stuff in fall, holidays/holiday service stuff in Nov/Dec, skiing etc in winter... not all might be directly relevant to each leader but it would give them an idea of how to plan and organize what to include in the scrapbook
2) family tree/family history. At least in cub scouting, there is a unit on family tree or history every year, it just gets a little more in depth each year. You can give examples of how to modify the pages to include the differences in requirements each year.
3) the ideals of scouting: cub scouting has 12 core values and the boy scout motto has 12 points, they can probably align pretty well so you can cover the spread of leaders from the young and old ranks. Each page can be for the scout to tell how they live this value and many have the potential to have relevant photos (assuming the leaders or parents are picture takers!)
4) a page for each year of scouting: Tiger, Wolf, Bear, Webelos 1&2, Tenderfoot, Second Class, First Class, etc...
I don't have any ideas for the Camping Bling at the moment, but I'll give it some thought!
still more green than buying a Pioneer scrapbook or plastic binder!) as well as the creative stuff! You can probably appeal to wide range of ranks by focusing the page/subject organization one of three ways: