I think we've all seen that I'm the "low budget" type. The TJ Brute beds look great, but they're way out of my budget right now. As of the last couple days, (thanks again to all y'all

) I've been hunting craigslist for pickup beds. Or I'll use some other creative keywords for searching. I found a couple days ago I think an old Chevy or Ford step side bed that would have been a good style to start with for $200. Now that I'm searching for it again, I can't seem to find it... I don't have the space to put it anywhere even if I were to get it right away, anyway...
My other options I was leaning toward was something like what you had mentioned as well. I was thinking I'd fab my own bed. If I can find a local steel supplier, I was thinking I'd build a truck bed using box tube, a wood floor, and either steel or expanded/perforated sheet for the sides. I'd probably use my stock tailgate for the Jeep logo to make a new tailgate as well.
It's also crossed my mind to start off with closing off the cab the way I want, stretching the frame to my desired wheelbase, then just going a little at a time with it, like building a wooden flatbed. If I was creative and planned ahead (nice wish on my part...), I could even use it like a "build-as-you-go" type of thing.