Raspberry Pi isn't available for over 6 months, and things aren't looking better. What devices are you using to run OctoPrint?
OctoPrint can be installed on just about any computer that you can install Python 3 on.
Raspberry Pi is preferred primarily because of OctoPi, a version of the OS with OctoPrint already installed.
If you want a small, cheap alternative then just about anything you find that will run a flavor of Linux (preferably Debian based) will work. A Google search for "raspberry pi alternative linux debian" found this which is as good a place as any to start.
What do you have lying around that isn't being used?
Other SBCs, the free broken laptop that still works as a server, Android phone, anything that has an OS and low power consumption.
A good alternative (that i will be trying soon) is TV Boxes that can run armbian, way cheaper than a PI and comes with 2 or 3 USB ports, network connection and wi-fi.
I didn't have a Raspberry Pi and was desperate for Octoprint (which is wonderful!), but I did have an unused LG V20 Android phone. I installed octo4a from GitHub and used an OTG adapter for USB and charger connections and I'm successfully hosting Octoprint from the LG. Performance is great. No need to root the phone to use this.
It also supports using the phone's camera, but I haven't got that dialed-in yet - on 1st quick attempt, it seemed quite laggy. Need to put some time into getting that going.
I'd still prefer to have a more permanently connected solution, so although this is working well for me now, I'll be looking for a compatible SBC to hard-wire into my setup.