MGN12 Gantry On 20 Series Extrusion - Need Simple Design

I am probably struggling so much with this because after buying a CNC 3018 recently, I dove into trying to build a DIY gantry-based CNC without much knowledge. I was very dissatisfied with the moving table for the Y axis, and the lack of rigidity using plastic parts for the frame in the CNC 3018 that I had.

I am guessing that there is a simple solution to my problem, but I just need someone with the experience to shed light on it. I have scoured Ali Express, Ebay, Amazon, and even Google images for ideas trying to find the most simple examples of how to design a gantry driven with a lead screw using readily available, relatively inexpensive parts. My budget is maybe up to a few hundred dollars, for the frame and the linear motion system (not including electronics, spindle, motor control system, but definitely including the aluminum extrusion, linear rails, custom plates, standoffs, hardware, brackets, etc.)

I see a lot of amazing gantry designs, but most of them seem to rely on custom plates that would eat up a good chunk of my budget, and they aren't always easy to change dimensions like the length of the axis and series of 8020 extrusion. So I the base of a gantry with two MGN12H blocks on each side that I think I could put together for a decent price, and still get decent performance. I'm nowhere near an expert, and if there is any waste, design flaws, or just a better alternative as far as price performance, please share your knowledge; it would be greatly appreciated!!

I am still trying to work out how to connect the lead screw to the base of the gantry, so if you can help with that part of it, that would also be really helpful. I modeled this in Fusion360, and I can share the project if needed, but it's really messy because I am terrible at making joints and I am learning all of this on my own.

Here is the base of the gantry: