1. Shop sales and coupons - Obvious right? Besides the tradition holiday sales times (Christmas, Labor Day, Memorial Day, etc) scrapbooking stores have big sales right around CHA time (December-January and June-July) They are clearing out last CHA's product to make way for the new stuff. Also, look for  promotions during National Scrapbooking Day (May)

Don't forget to watch for photo printing deals, Snapfish and Shutterfly offer lots of great promotions throughout the year.
*Beware of buying just because it's on sale. You can blow through your craft budget with products you're not really in love with*

2. DIY - Some products are easier than other to re-create, but many are easy to replicate with a little time and a trip to the office supply store/printer. The best part about DIY embellishments is that you have more freedom with colors, themes, and amounts.

Here are some tutorials I've made replicating popular scrapbooking products.
DIY Transparency Alphabets
DIY Foldover Tabs
DIY Stitched pockets

Page using the DIY transparency alphas

3. Check big box stores - Joann's and Michael's only carry certain name brands, but with their weekly coupons, you can get some great products and tools for cheap! I tend to use those for staple products, cardstock, ink pads, colored cardstock, paper cutter blades, etc.
* Don't forget your coupons!*

4. Warehouse Sales - If you have a favorite brand, check out their blogs or Facebook pages to see if they do a yearly box sale. Most of the companies offer a great discount and a partial list of what may be included. Some also have brick and mortar places set up, where you can pick and choose which products you want.  * My favorite warehouse sale is the American Crafts. It's located in Utah every years and is open from Thanksgiving to New Year's. If you have an opportunity to go, I would highly recommend it. Not just because of the great prices but because they have four different brands located there (Crate Paper, American Crafts, Studio Calico, Pebbles) We shall see what 2014 brings with their recent acquisition of Pink Paislee and Imaginesce*

5. Be Picky - When a new line rolls out that I am in love with, I have a tendency to want every.single.piece of it, especially the papers (my weakness) Logistically, that is impossible to afford and store in my less than 1000 sq. feet apartment. I tend to window shop the line. Review each piece over and over online and narrow down my selections. I usually end up with 3-5 papers and 1-3 embellishments. This cost is at most $20, which is much for affordable then the $75+ of the entire line. Also, Before making an embellishment purchase (meaning anything other than patterned paper), I ask myself, "How long with this last me?" For example, I can spend $4 on a roll of washi or a pack of decorative brads. Depending on the colors, themes etc, one will probably last me way more than the other.
*Try to buy products that can be used for more than one event/category/holiday.*

6. Tools - In the short run, tools cost more, sometimes a lot. Over the course of a year or more, they can save you lots of $$$. Specifically, an electronic diecutting machine (Cricut, Silhouette, etc) can allow you to make alphabets, stencils, even your own patterned papers, which reduces your need to buy. Color mists and inks can also help you create unique backgrounds, change embellishments and enhance products your already have.
* Tools are great for DIY embellishments.*

7. Sell/Share - There are Facebook groups and message boards where you can sell your unused products and boost your craft budget by a little. You can also try to sell locally on Craigslist or at your local scrapbook store. Also, you can sign up for swaps or share a pack of embellishments with a friend.

8. Buy with a project in mind - Mindlessly buying can lead to unused products and wasted money. I used to do this. It's cute, I'll buy it. I'm much more conscious of what products I'll be using for which projects. This stops me from buying just because it's cute or trendy.

9. Know Thyself - Go back through your scrapbooks and look at what products your gravitate towards. Think about what you're always running out of, or your favorite things to add to a page. Stick to those things. If there are certain products that you love, but rarely end up using on a page, keep those purchases to a minimum or not at all. For example, I have a hard time using ribbon. I love it, it's pretty, but it rarely makes it onto a page. Once I realized this, I stopped buying ribbon. 
*If you are new to scrapbooking and aren't sure what products to use or which ones you like the best, I would recommend purchasing from a kit club which will allow you to try a sampling of products without a huge financial commitment. *

10. Splurge - Every once in awhile, a product comes along that I am just dying to use. It doesn't follow my 9 previous rules, but for whatever reason, I just can't talk myself out of it.  Save up your craft budget and spend it on that thing you've been dying to have. The reason I say this is actually a mental thing. Budgeting can be hard. Giving up freely spending isn't fun. And rather than try to supplement with products and DIY's that aren't going to satisfy you, it's ok to splurge every once in a while.