The office of the Louisiana Secretary of State has compiled a list of accordion builders from Louisiana, though Maz has pointed out some of the best known.
The link is listed above. Also, Jude Moreau (who frequents this board) is a well known accordion maker from the Texas side of the Tex/LA border.
Weltmeister's are German made boxes, and not too bad, definitely better than a Hohner. If you can afford a LA box, by all means get one, but a Weltmeister would be a good starter box. If I remember correctly they go for around $800 or so. I had a Weltmeister 3 row and loved the thing, shouldn't have sold it. As far as accordion makers, the only ones I have tried are Bon Cajun, Martin, and Savoy, I personally like the Bon Cajun, and Martin boxes, but old Savoy's are apparently really good. Martin accordions a slightly heavier I think, so you gotta have strong hands to get a good sound out of them, but it's worth it, they are loud, and have a good tone to them.