I use a regular zippo with a KGM Thunderbird butane insert. I think it's the most economical route. Z-Plus! makes a jet torch butane insert, but as far as I'm aware, only Vector KGM makes a soft flame butane insert. If a warranty is important to you, the Xikar EX product line is nice too, they can be as much as $50 though.
I'm currently in the market for a 'im double corona', but seeing as I live in Ontario, it's difficult to locate such a specific item without going to an auction site.
As far as I can tell, those are the best soft flame lighters, unless you want to purchase matches, which are also a retro option. Colibri has a soft flame called the Wellington, but people frequently complain about Colibri, and I have no experience with the brand.
P.s. I just noticed that all these lighters I recommended use flints, with the exception of the Xikar EX, which is piezo if memory serves me correctly. So if changing flints is something you don't want to do, the Xikar may be the best choice.