My advice would be to go down the route of CBT Nuggets, buying secondhand books and teaching yourself, some subjects can be a bit dry but its all doable. Set up GNS3/EVE and use it as your home lab, best way to learn is by trial and error. I took the Juniper track, currently looking at Cisco and Aruba now, but by and large the principles are the same, as suggested, you could take a vendor agnostic course to give yourself the fundamentals?

There is a massive drive towards automation so any python/ansible etc. skills would be major bonus.

If you've an interest in network engineering, I think given the current market it is one of the best routes to take in IT, although I am biased! There are a multitude of areas in which you can specialise in once you have the fundamentals.