If you can contact the appropriate Re-enactor units in France and Mexico, you might solve all manner of problems--and costs--for extras, fully and correctly costumed--and only pay to defray travel costs to your location.
A copy of the Camerone enclosure would be a fairly cheap build--certainly cheaper than either of the US Alamo reconstructions!
The script, however, is everything. If it doesn't engage the otherwise ignorant audience, any finished product won't have the "legs" to make it a profitable project. Mind, it should play in Mexico and in France to good audiences, and if you can figure out what that would translate to in plausible box office in those two markets, that might be the budget to shoot for. If you can make it all back in those audiences, the profit will come from worldwide distribution, cable, and DVD sales. I PROMISE to buy one, so there's $19.95 USD right there…on paper.
Danjou should NOT be the main character. If it's all about him, his death will be the high point of the film, and all the rest a long, loud denouement that will not satisfy the audience. The protagonist should be one or all of the (three?) survivors. While their actual biographies--to the extent these are known/available--should be the starting point for developing their characters, you should not be above fudging the facts, very much as the Cy Enfield did for is script of "Zulu."
"Hook" was no scoundrel, and the rest were manipulated to help make a good story. Go thou and do likewise (especially if the facts are unknown or unremarkable enough not to be useful).
Nappy III should be the off-stage villain of the piece, the one to direct all modern audience antipathy to "Imperialism" towards--and not unfairly or incorrectly. US sympathy to Juarez and his cause should also, rightly, be alluded to (so the audience will know where WE were in all this mess), but as this little kerfuffle of a Civil War was going on at the moment, we weren't able to do much more than sympathize.
While costs used to be a lot cheaper for films shot on location in Mexico, and there was (is still?) plenty of competent technicians at the old Churubusco studios of their own film industry, I don't know that actually shooting down there would be such a good idea. Between drug wars and "La Mordida," the insurance costs alone could be prohibitive, and the real danger of Yanqui cast and crew being subject to extortion (kidnapping and other threats--or actual occurrences) might make even a short shooting schedule more trouble than it's worth.
It seems, though, that financial support, at least, might still come from Mexican interests on both sides of the Rio Grande given the genuinely patriotic nature of such a project. I don't know how friendly their Government would be to such a project (unless you give Nappy III Donald Trump's hair).
But if you can get a pretty good estimate of the actual production costs, maybe this is something that might receive at least some backing through Indiegogo or Kickstarter, though I don't have any idea how "international" those services are and whether investment by supporters of the project--who are distributed worldwide--would be able to find out about such programs and contribute meaningfully.
I suspect that if the Foreign Legion were itself approached, they might be able to offer help, if not of a financial nature. Maybe they'd let you make an authentic copy of Danjou's arm, if not actually use it, and other information to help add color to the film. At the very least, if there was some buzz that the Legion itself was in favor of this film, that would get some unusual promotion.
You could at least count on all current and former Legionnaires buying a ticket!
Then again, whoever might speak for the Legion in such a project would want to see a script first, and they'd have to be pleased with it, so that might be a problem depending on how your script treats the FFL. And, if they just hated it, you certainly would get not only no help, but they might even pan it before you've shot the first scene.
Hope you already know somebody who knows somebody who knows how to approach the FFL and/or French Government delicately to see if any of this particular bit of blue-skying is actual practical.
Maybe you'd have to shoot in France--if not Spain--to most affordably bring all your assets together, but clearly that's a decision you can't make until you know what the money situation is and--minor detail--have a script that's smokin'!
If you think of this as "Mexican Zulu," you should do very well. Strong performances from one or two Big Names, and some very good, but not yet "big," performers in all the character roles, plus tons of action--and just a touch of Blarney--and the whole thing should work.
I'm ready for my close-up now, Mr. DeMille….
TVAG
finally dips his toe into the world of Aeronef.
