If you're looking for a quality knife for $12 consider purchasing Mora's Companion #11863 Carbon Steel Knife that is manufactured in Sweden. This knife was brought to my attention by a friend, who highly recommends this knife due to its durability under heavy use with the non-edge side of the knife being used as a FireSteele striker to start fires. The knife's weight of 2.7oz is light for a quality 4" blade with a 8-1/2" overall length. Cut and paste the following description into Ebay's search engine to find this knife being offered by Oak Cutlery, MORA OF SWEDEN 11863 (840MG) COMPANION MG CARBON STEEL BLADE KNIFE.
Pictured is a comparison between a $33 M9 bayonet and a more expensive Ontario Knife Company M9 bayonet. For those looking for a less expensive alternative take at look at the bayonet being sold by Szco. I purchased this bayonet from amazon.com based on reviews and was not disappointed. I also included a picture of the bayonet attached to a mid-length AR-15. Based on your budget either bayonet is a must have addition to your kit as a fighting knife.
Purchase Cold Steel's Delta Dart with triangular spear point for a light weapon with superior penetration capability. The lightweight plastic design makes this self defense weapon easy to carry for any situation. Purchase this item at MidwayUSA for $3.99 at the following link, Cold Steel Delta Dart Fixed Blade Tactical Knife 3-3/8" Spear Point Zytel Blade Zytel Handle Black. Attached is the product description from Midway's website, "Its comfortable handle is knurled for a positive grip and the butt is smooth and rounded, so it's perfect for both thumb and palm reinforced positions. The Delta Dart is made from Zytel, which is this super tough material that, when combined with the Dart's sharp point and triangular cross section, accounts for its phenomenal piercing power." While you're at Midway purchase the sheath that is sold separately at the following link, Cold Steel Delta Dart Neck Sheath Concealex Polymer Black. At this price you should include one of these in all of your bugout bags.
Pictured is a Gerber MP600 Multi-tool recently purchased for $29 shipped on Ebay (used). Vendors normally sell this tool for well over $60. The MP600 is a great tool for use at the range, in the field and has a number features for use with the AR15. The front site post adjustment tool (extended in picture), scraper and non reflective surface make it handy for field use. The only complaint about the system is the replaceable carbide blades are sometimes crack. Features include: Needlenose Pliers, Wire Crimper, Wire Cutter, Front Site Tool, File, Fine Edge Knife, Serrated Knife, Phillips Driver, Small Flat Driver, Medium Flat Driver, Large Flat Driver, Ruler, and Bottle Opener. Include the MP600 in your range bag and all of your gear.