There is a Capri Camper selling for $3950 (in New Braunfels). It apparently has air conditioner, heating, jacks, shower and porta-potti...bring an local RV tech with you; it'll be worth the ~ $100
I wouldn't rush into an fancy aluminum camper buy with only weeks allotted to research! There aren't many if any aluminum-framed pop-up campers in decent shape selling for less than ~$6,000/$7,000 that I could find today. I wouldn't even look at a used camper (pop-up or hard-side) that didn't have a full aluminum frame superstructure and non wood-backed fiberglass skin: tub, walls AND roof, and those genre *used* are selling in the ~ $8,000 ~ $12,000+ range in decent shape. Caveat: UNLESS it is a camper you can easily inspect at an extremely attractive price, like that $3k used Capri. We look at used (and some new) truck campers this way: we assume that THEY ALL leak to some degree; so the less organic materials used in the superstructure, the better
$8k to 12k for a pop-up (or, any used camper) is a big investment that you can't afford to make a mistake on.
On edit:
And, bear in mind that you don't want to try and escape Central or South America without that "huge piggyback" registered in your passport (if you ever want to go back to said countries in the future) !