MX-FS-03V one transmitter to many recivers
They only cost £1.69 (from here) as a pair and most of that cost will be for the receiver (because they are more complex than the transmitter): -



Transmitter at the top and more complex receiver at the bottom.

So, buy a few (a small outlay of £10) and experiment. There appears to be no data sheet for this device so it's impossible to say if the adjuster on the receiver will tune it precisely to a different transmitter but, for substantially less than the money I'd charge for giving this advice professionally you could find out yourself.