sliding window maximum
In the worst case, there is no algorithm with better space complexity than storing all data points from the past hour.  So, I think you should focus on optimizing time complexity.  A reasonable data structure would be to store them in a balanced binary tree, keyed on timestamp, where each node is augmented with the maximum price over all descendants of that node.  This achieves $O(n)$ space, if there are $n$ data points within the past hour, and $O(\log n)$ time per data point that you receive.