Some of us work directly with charterers to give them good deals compared to many of the companies. I wouldn't necessarily call them cheap charters - like agrimsrud said, often you get what you pay for.
Also, sign up for the email lists from individual boats, since I know I send out occasional deals. Also worthwhile to email or message an owner with your dates, and ask what sort of deal you can get - or make an offer! Especially true for last minute trips. Like Manpot said, you're going to end up shopping around a bit, but its fun, and I think, worth it!
Feel free to check out my site (
www.syTimeWillTell.com) and send me a message!
-Peter