Hello Everyone! New member here!

So where do I begin...I've been a hobbyist wood worker my whole life and I want to build a cnc router machine to enhance my projects.
I've have been researching diy cnc machines for a couple a weeks and I have to say I'm overwhelmed with the options and opinions of everyone and every product out there.
Let me start with my build specs. I want a work area of 4ftx4ft and it will be on an existing workbench, so I can basically go to hardware store and get a 4x8 board cut it in half and let the machine start cutting what I need. But like everyone I have a budget, and honestly the lower the better.

So lets just start with the frame first and you guys can help me with electrical components later.
I originally wanted to make my frame, gantry arms, z axis cross beam, basically the whole frame out of wood. Then I thought, let me do this the right way the first time. Wood is great, but not for everything.
My concern is the flex of wood and I want a precise cutting machine!
So i thought, okay, let see what's out there made from aluminum, its light and strong with the right thickness, and I came across regular aluminum flat bar 3/8-1/2 thick that I would use to make the gantry arms and the cross beam, but Its kind of pricey! So then I looked into T Slot from like 8020.com, and that website has so many options I don't know where to start, but I'm concerned about that flexing as well, I do like their linear bearing that can substitute buying linear rails for the gantry arm attachment but also kind of pricey. And steel is too heavy so I haven't even really considered it.

So guys please help me with a material to build this frame that is strong but on the cheaper side.