There are a number of "sidewinder" mods... most well over $100. As you know, the Zenesis Sidewinder and Chel's MicroStick may be the most well known & popular.
There's the SvoeMesto "Sticker" in both standard size and mini... which is a sidewinder base or conversion (for lack of a better description). Although not inexpensive, allow a wide application range.
The SM Sticker type adapter
may be the next thing to get cloned by China, as it perhaps has the broadest application. Figure well under $25 if they do it. A few more months? Maybe.

A ECF member named "bapgood" has been making
his own version of a sticker, with a Kick fit to it. For sale? Not a clue - you'll have to ask.
The Smoktech "Sidewinder" (which is a cheap copy of the
Great Lakes Vapor (GLV) mod)... is not really a true side by side, but more an offset, where you don't save much in height. (There are a few generic GLV copies on FastTech too, for around $20)
There are several discontinued sidewinders - lost to poor sales/marketing I'd imagine - like the ZiMoshi... which as I understand, came out about the same time as the GLV, so not a copy.
The
Madvapes Gripper is a super cheap sidewinder, but won't hold anything larger than a 9 X 45mm cartomizer. Still, for $10, a neat little device.
There's a China mod (R80) with a hinge - it's really more a pipe mod (and will accept large diameter attys in pipe mode) that you can use as a side by side - but in the sidewinder form, the best you can do is attach a small diameter clearo.
There's the Vapage Vmod bottom feeder... a sort of econo-Reo that (sort of) qualifies as a sidewinder. If you look around, you can usually pick these up for 40% off or better.
There's more... but
I'm done.