You're not gonna have much luck getting a new Shoei, Arai, AGV, etc for less than 400-600 bucks....Sorry, but in my personal opinion, it really is a case of "you get what you pay for"...Most of the more expensive helmets are made from lighter stronger materials than the thermoplastic shell that your TK-9 is made of. For example, a fiberglass shell is better than a thermoplastic shell because whereas the plastic will break and then be completely done, fiberglass flexes and bends then breaks, kinda like a tree branch. If you ever take a tree branch and bend it until it breaks, you'll see that it takes a lot of energy for it to actually tear. Once it does, yes there is a break in the branch, but the fibers that make up the tree branch still have all their strength still. You can't get that sort of thing with plastic.
The other thing is, a lot of times the benefits of a "better" helmet aren't just how well of an impact it takes. Lighter weight helmets create less strain on your neck. Lighter materials are more expensive. Quieter helmets leave you more comfortable. Sound-deadening material isn't free. Well ventilated helmets require a fair bit of engineering and testing to actually perform as hoped for. All that work isn't free. Helmets with removable interiors can be cleaned up a lot more easily and faster than helmets without removable lining. The system to hold the lining in place but also allow it to be removed isn't free either.
Pretty much any company can make a helmet that survives certain impacts per DOT or Snell standard. Not every such helmet though will actually be comfortable to wear.
I say this, not to belittle your choice of helmet or to crush your hopes of finding a top grade helmet at a really good price, but to maybe shed some light on why these top grade helmets actually cost as much as they do.
Another way to look at it though, would be like this. Of all the gear that you could possibly wear when you ride, the only thing that protects your brain is the helmet. So you kinda got to ask yourself, how much is your brain really worth to you?