Welcome Jack,
Man I wish the internet had been around when I started brewing cans.....
As you've got a temp controller, proper yeast is the next step i'd advise (12deg for lager, 18-20 for ale) 6-8 bucks a sachet, and as Pratty said you can keep them going from beer to beer to lower your costs even further. You'll be surprised at what a proper yeast for style can achieve. If you're not brewing in a fridge, then you'll have to wait for winter to make lagers.
Dry Hopping was another revelation to my kit brewing. Don't even bother with the 12g packets at Big W or the homebrew shop for $3, find a hop flavour you like and buy 90-100g for about $12.
Steeping grains will add heaps of flavour and mouthfeel to your beer, and you can do it on your stove top with a regular pot, so long as you have a thermometer.
These 3 things will make the awesome beer you're already making even better, for no capital outlay- just the materials. Are you starting to hear a common thread???
Hope this helps,
RB.