You're young, the cheapest option would be a dirtbike. Ask the majority of this forum and they will probably tell you they started on a dirtbike.
But if you want to build a truck. I agree with what
@Motiracer38 said above.
What he meant when he said floppy beams, was I beams or Twin Traction Beams (TTB for short).
Also known as Whoop Scissors.
Ford built trucks and SUVs with this amazing front suspension up until the late 90s.
You could get a ranger up until 1997 with this suspension.
The full size F150 and Bronco ran this up to 1996.
The desert community has been modifying beams since the dawn of time, which means you can find plenty of used parts if you scavenge Craigslist, Marketplace, Race Dezert, and the classifieds on here. And there are tons of build threads on beamed vehicles from mild to wild to read and learn from.
All the cool kids have Bronco's these days which means prices are way up.
You can still find good deals on F150's and Rangers with this suspension.
The wildcard pick would be a 1991-1994 Ford Explorer. It uses the same Dana 35 beams as a 4wd Ranger. The big bonus is that the rear end is spring under from the factory. The big downside is the majority you find will most likely have transmission issues.
And check out this build thread:
93 Explorer Prelanding Camper
He doesn't even have coilover's up front. Just Bilstein 5100s and 4" Coil Springs and the thing boogies through the desert.
Cookcraft also makes a rad rear shock mount for Explorers that allows you to get some takeoff Raptor shocks and throw them on the back.
