For little to no money, you can rig up an old (or new) PC fan to an old DC adapter (like the kind you plug into a cell phone, router, modem, etc...) Just make sure the power adapter is 12v and the mA or A (milliamps or amps) are at least equal to or more than the the mA or A printed on the fan. Remember, .1 A is equal to 100 mA and 1A is equal to 1000 mA, so if your fan says 500 mA, your adapter needs to be greater than or equal to .5 A (or 500 mA).
Here's a thread
https://www.rollitup.org/grow-room-design-setup/196833-3-wire-pc-fan-outlet.html
To sum it up though, here it is in 8 easy steps...
#1 Get your adapter (wall charger)
#2 Get your PC fan
#3 Check to make sure the adapter is rated for 12v and the A or mA on the
fan is less than the A or mA on the
charger.
#4 Cut the "device" part of the charger off as close to the end as possible (the side that plugs into the phone or modem or whatever) and strip the wires.
Don't cut off the part that plugs into the wall!
#5 Cut the 2 or 3 pin connector off of the fan (the end of the fan that connects to the computer, not close to the fan itself) and strip the wires.
We're only concerned about the red and black wires. If there's a third wire (most likely yellow), we can ignore it as it won't be used.
#6 Look at the wires coming off the charger. You should notice that once you separate the 2 strands from each other and strip them, one of the wires will have a white stripe and the other will not.
#7 Connect the
RED wire from the fan to the wire WITHOUT the white stripe (this is the live).
#8 Connect the BLACK wire from the fan to the wire WITH the white stripe ( this is the ground).
*NOTE* Sometimes the wires coming off the adapter can be reversed. It's very uncommon, but if you wire your fan as above and it doesn't work, switch the red and black wires.
I love using PC fans because I'm in IT and there are always plenty of spare parts laying around... I love free shit!