The Exell A1611 was the original aftermarket replacement for the 206A. Back in 2005 - these were like 6-8 bucks a piece. And they worked like a charm.
But then reports started coming in that they were starting to be manufactured to wide - and were getting stuck - or just wouldn't fit in the mics.
And now they are 25 bucks a piece!
There's a couple of combos/approaches - I'd study the battery selection at your local hardware store - see if they stock anything useful.
I've used the Energizer A23 - they're 12V - but that's fine for that mic.
The A23 is a little short, so it it needs a little stilt in the battery compartment...also a bit thin - so I wrap it with electrical tape to get it to proper width.
But only 4-5 bucks a piece - and available in most grocery/hardware store battery racks.
Another old school hack - drill a hole in the mic and solder a snap on 9V battery to battery contacts - just tape the battery to the mic. First ME-120 I owned had been "modded" like this...not recommended - your signal is going through that wire!