Buy wood. The charango’s back was traditionally the shell of a quirquincho — an armadillo — and instruments made that way still turn up for sale. A carved wooden body is what is made now, it is more stable in every climate the instrument was not designed for, and it will not create a problem at a border. Nothing about the music requires the shell.
Which instrument in the family
Charango is one size among several, and the names are not interchangeable. Smaller instruments — walaycho, maulincho — sit higher and are tighter under the hand; the ronroco is noticeably larger and lower. Sellers online are not always careful about which one a photograph shows, so check the scale length rather than the word in the listing. If you want the instrument the tuning on this site describes, you want a charango.
Ten strings, one narrow nut
Five courses across a nut the width of a thumb is the hardest thing to make well on this instrument, and it is where inexpensive builds fail first. Look straight down at the nut: the two slots of each course should be evenly cut and evenly spaced, with the pair close enough that a stroke hits them as one and enough room between courses that it can clear them. Uneven pairs make every figure on the rasgueo pages harder than it should be, and no amount of practice fixes a badly slotted nut.
Then the tuners, then the neck
Turn all ten. Nylon at this scale length holds a lot of tension for its diameter, and tuners that slip are the difference between an instrument you pick up and one you argue with. Then sight down the neck: it should be straight, and the top should not be visibly pulled up behind the bridge. A charango is small enough that a bowed neck is usually terminal rather than adjustable.
Play it before you decide
Take one shape — a C major from the chord library is enough — and strum it hard. You are listening for two things: whether the octave string in the middle course speaks clearly, and whether anything buzzes when all ten strings are moving. A charango that sounds thin on a full stroke is usually telling you about that one string, which is the cheapest fault on this page to fix.