How to check AWS spot pricing automatically?
Spotted an open source tool called autospotting that just might help with this:  


  Once enabled on an existing on-demand AutoScaling group, it launches an EC2 spot instance that is cheaper, at least as large and configured identically to your current on-demand instances. As soon as the new instance is ready, it is added to the group and an on-demand instance is detached from the group and terminated.


We have this in our to-do pipeline, will be able to add more context once we finish that.

Update:

Another tool that was recently demo'ed in a conference was mapbox/spotswap

This works slightly differently. It monitors a normal ASG with either On-Demand or Reserved instances and then, if scale arises, bids and provisions spot instances of similar compute level on a separate ASG.