What would you recommend as a "pipe with MQ-ish semantics" to use when "the message order was not important, there was only one producer and one consumer and the volume of data was not extra-ordinary", but you do still want the core premise of an MQ — reliable message delivery in the face of faults in the producer and/or consumer?

We actually have a use-case that exactly matches this. One service makes [stuff], the other service consumes [stuff], both services are "immutable infrastructure" with no local stable state storage, and [stuff] is individually too small and frequent to be affordable with IaaS managed-MQ per-message costs — but batching messages into reasonable chunks before send means potentially losing up-to-a-batch worth of messages if the producer dies.