I have used the ancestor to the Logan 860 and found it just barely acceptable for professional use. The stable, well-captured, sliding puck pushes it just over the boundary line between cheaper and better matte cutters. Most other Logan stuff is junk and will be abandoned soon after purchase.
For the small 2:1 and 3:1 ratios you mention, the only reasonable solution is to purchase dirt cheap imports in high volume. There is simply no way you can custom build frames at that size and hope to make a profit, assuming you want to value your work at more than a fraction of minimum wage.
FWIW those 16" wide sizes are under the smallest realistic "impulse buy" or "carry away" sizes. As you analyze materials usage, you may find there are larger possible sizes that can be built for the same price as smaller sizes, taking into account things like wastage. Always build the biggest possible size for the cost of materials. I have found 34" wide is a very attractive minimum size for panos that does not inhibit impulse buys due to size.
Yes, you can use metal sectional frames, but there is a curious problem with those things. In high end galleries, sectional framing treatments can sometimes look impressive and even somewhat dapper. However, in almost all other cases they manage to cast the artist as a low budget hacker. Think 30 man show at Joe's Java. It's hard to explain, but it's true. The venues I classify as competent sales outlets don't like them, and in fact many won't accept framing treatment that use glazing, aka glass or plex coverings.
