I think AIOs are nice and a great way to start. They are extremely limited in space for things we do out of sight. If you want to keep a few sea things it's a great way to go but for long term growth somewhat limited.
I had a nanocube and quickly went to 20, 30, 50, 75, 240 and 75, 240 and 180, 240,180 and 75. It's like an addiction for some of us.
From a cute little sump under the tank to an entire room of stuff gurgling and whirring all the time.
Save yourself and run away now.
To do this hobby cheap learn to make and do. A Waterbox 50.4 costs $1500. A Marineland 75G tank and stand is $500. You drill it yourself.
You can make a stand and cut that price down too.
Tanks come in many sizes these days, cubes hexagons, rectangular, bow fronts.
My 180 plus materials for the stands I made was about $1500 not too long ago. It was a reef ready tank from a LFS.
Then there is the used market. People quit all the time and take 20 cents on the dollar they invested. You can get a quality setup with lights and all for $1500. With rocks and livestock often.