Here's the secret to legit, DEEP discounts:
1. Buy online at 20% off.
2. Buy enough to get free shipping.
3. Lastly--the most important part--
buy the larger boxed sets with built-in savings.
Examples:
Deff Dread Mob
Retail: $85
20% off: $68
Price of kits sold separately: $99
Total Savings: $31 (31% savings)
Adeptus Astartes Strikeforce
Retail: $230
20% off: $184
Price of kits sold separately: $290.25
Total Savings: $106.25 (37% savings)
Crimson Slaughter: A Dark Vengeance Expansion Set
Retail: $135
20% off: $108
Price of kits sold separately: $171
Total Savings: $63 (37% savings)
If you pay taxes on retail purchases, you can also factor this into your savings to make yourself feel even better

Obviously, you could sell what you don't want on eBay or trade with/sell to friends for increased savings. This is how you save money on
GW without waiting for once-in-a-blue-moon sales or rare, lucky finds.