It is definitely worth your time to attend some community college machine shop courses to learn the trade. They have both the machines and instructors used to teaching beginners. Once you get to know the instructors, talk to them about buying a machine.
When you are using the school's machines for your class projects, use as many different machines as you can to see what is different and which you like the best.
There are lots of places to buy used machinery. DON'T BE IN A RUSH TO BUY. Study the machines at school and learn what is good and what is bad in used machine wear. Remember, you are not building fine instruments so you don't need a perfect machine, just one that runs well without serious problems.
A beer can scaled (1/5 scale) 13" mortar would be 8.6" in diameter with a 2.6+" bore. This is a pretty heavy piece of steel. The image at the bottom of this post is a 1/3 scale 8" M1861 mortar bored 2.25" but it could easily be bored up to beer cans. It was made from a piece of 6" steel and weighs (tube alone) about 80 lbs. A 1/5 scale Dictator (M1861 13") would weigh at least twice that counting the mount and require a significantly larger chuck to hold. It could be turned on a face plate if the face were drilled and tapped for mounting bolts. These holes could be plugged when no longer needed.