If you aren't looking for something show quality, there are lots of things out there. However, if you want something leather and fancy looking, it'll be $100+.
I won't state my opinions about bitless in depth, but just know that it's VERY hard to get or keep a horse light in a bitless bridle. I've ridden bitless with my mare for the last 4 years and I've just recently been forced to find a bit that she likes to be ridden in. She had started running through the bitless thing on a regular basis because she had discovered she could. There was nothing I could have done differently, she just figured it out and once that happens, you can't go back.
To my mind, bitless is not the most gentle since you have to be so much more "hands-y" with the horse to get a message across. I think a bit is much gentler when the horse is correctly trained to accept one, the rider has gentle hands, and the bit is chosen for it's clarity of signal.
Anyway, here are some options for you:
This is the kind that my mare learned to run right through. It's very gentle but since it does tighten around the nose when pressure is applied, it's a little harsher than just a sidepull of some sort. BITLESS BRIDLE Indian Hackamore Bosal Black w TURQUOISE Nose Band | eBay
Same thing with a little more "bite" Rope Bitless Bridle Hackamore-Indian Bosal/Side Pull | eBay
I currently have this one (in the first style) for when I want to ride bitless or when I'm giving lessons. My mare respects it better because of the knots and it doesn't have the tightening action of the first 2 options. Side Pull Rope Hackamore Bitless Bridle Attachment | eBay
There are a lot more options than just those but those are the ones I've tried and liked. They all need you to have a bridle, reins, and for the last one a curb chain, but buying all that will probably only run about $60-70 if you buy everything brand new.
People are probably going to suggest a hackamore (a bitless attachment that relies on leverage, all my links say hackamore in the name but they aren't true hackamores since there is no leverage involved) eventually but I'd strongly advise against one. You can do SO much damage with a hackamore, completely unintentionally, and that scares me.