The list if pretty short if you're looking for a good knife for $10 or less. Depending on where you live, the local laws, how you dress, etc. and if you need a folder or can live with a fixed blade I can think of a few choices. For folders the Opinels are indeed very good knives. They have a variety of sizes in several different steels; the carbon ones take a very good edge. They lock securely and don't look tactical at all. Not easy to deploy one handed though. The Cold Steel Kudo is also a good option. It's a copy of the African Okapi and is somewhat on the large side for a folder (again, check your local laws). It's a bit 'quirky' to operate but very strong with a blade of decent steel.

For fixed blades you can get a Mora for right around $10 if you shop carefully. They're great knives for the money, maybe great knifes regardless of the price. The steel is good and they come shaving sharp (generally, it varies a bit). Lastly the Cold Steel Pendleton Lite is around $13 and sometimes it dips under $10 on Amazon. It's a screaming bargain if you can get it for that price. Last time it got down under $10 I bought five of them.