Cheap and dirty you say? Challenge accepted!

• Second hand mechanical keyboard from craigslist: $20 or even less if you're lucky
• Pro Micro MCU from aliexpress: $5
• 100 pack of diodes from aliexpress: $1
• Assorted lengths of wires: $2

Desolder all the switches you need from the old keyboard and reuse the keycaps. Make a grid to mount the keycaps in by cutting out squares from cardboard and gluing several layers together, and stick the switches in the holes. Handwire everything and connect both sides to the same MCU, which should work as long as you don't have too many rows and columns. Flash the MCU with QMK.

The trick to switchich to ortho layout, or anything else vastly different from what you're used to, is to go all in. If you only use one at home and keep using a "normal" keyboard at work you'll likely never get used to the new layout. For me it took about 1 week until I could write comfortably on split ortho and a couple of more weeks until I would type at my old speed. Now that I'm used to it I have no problems switching between split ortho and traditional keyboards.

Little Keyboards, Beekeeb, SplitKB, Keebio, Boardsource have kits at various price points. Cheapest will be to build plateless and caseless

If the keyboard is too cheap you might end up thinking split is bad, but the real reason would be cheap switches or something.

Buy a keyboard you can sell used or borrow one from a friend.