If you have low traffic, then using a ready-to-scale later solution could still be cheap, and won't force you to re-factor your solution when scaling issues will start knocking at the door.
Google PubSub, AWS SQS are there to provide easy solution for you. If you want to avoid vendor lock-in, RabbitMQ sounds like a very reasonable choice, and could be cheap for low volumes (look at CloudAMQP plans, for basic but fast and reliable pubsub, the free plan could maybe be enough for you (and Rabbit MQ libs are available in any languages) There's a small learning curve, but then you'll be set for a long while!