What if I took a small portable speaker and a mini mic and connected them via a 3.5mm coupler? (twin female ends)
Would this work? If it does its about $5 to make...
edit: and the speaker you were using has an amp inside it...? (I think)
I'm almost clueless about this stuff, but I know you need a mic+amp+speaker combo to make it work
Electronics guru needed
Hi. I am almost a Mechatronic technician so listen to me

When you say speaker, you can see a bunch of stuff. You can or can not have a amplifier inside, so open this damn plastic box and look, if have a circuit board with some heatsink, congratulations you have a amplifier, then you can discover where is the input of it and plug a microphone. But the amplifier need a energy source, and if you are talking about an speaker with a wall plug, this can be hard. Or not.
For shure, will be the amplifier board and a transformer board, or all built in a single board. DON'T CUT THE BOARD.
You will need to look for the voltage of the amplifier, or the output voltage of the transformer, if it's 12V 9V some like this, you're done, take a battery plug on it instead of the transformer and it will work.
Now, if this speaker don't have a amplifier, you can build one with an LM386, it's a integrated circuit board that can operate in 6~9V and have a nice amplification.
Any question PM me

I'm bulding an LM386 amplifier and voice modulator.