If you aren't looking for one to haul to shows, just one for at home, I would second those who say to call a carpenter. Two of my friends at the barn (an eventer and an AQHA rider - both have multiple saddles) have had carpenters make trunks for them, but they don't take them to shows.
I have one that I bought used from a lady that had it made by a guy, and it fits in my horse trailer (wheels up the back ramp) which is great for shows because I don't have to pack lol. I can fit up to two dressage saddles in my trunk and most of my stuff, except blankets. It's got a topper for my boots and helmet.
But yeah, find a guy to do it for you, way cheaper than going through a tack trunk company.
They say money doesn't buy happiness -- well happiness doesn't buy horses!