On the budget front, I'd say the Kolcraft double umbrella. Trouble is, if this is the last trip where you'll need it, your kids are probably too big for this one. Perhaps a Schwinn SC700, but I've heard that there is an issue with a bar that goes across the back being a bit uncomfortable. The double version of the Lightrider, the Duo Rider from Graco, is considered lightweight by some people, but it runs about 25 lbs., IMO, not light. (Also, it is very wide, and has a bad rep for durability.) The Graco stadium-seat double, the DuoGlider, is generally considered the lightest-weight domestic tandem; it weighs a whopping 32.5 lbs, and does NOT fold very compactly.
NOTE: I knew there was a lighter Graco double, but I couldn't reference a US dealer for it. I finally found it, but it looks like it's been discontinued on the US market. It's the Graco DuoLite, 18 lbs. This is the double version of the CitiLite; the basic design is similar to the Combis. You can get them from a dealer on eBay for $95, just search for duolite stroller.
Another possibility might be two Chicco Caddies, hooked with stroller connectors. The Caddy has good resale value because it is larger than average and reclines. Unfortunately, it is not made in a double model. (Come to think of it, I'm not sure Chicco makes ANY doubles.)
When you are talking about really lightweight strollers, you have to have good suspension to get good performance with heavy loads. That is where the price difference comes in; cheap strollers tend not to have the suspension you need to be able to easily steer two kids. They stiffen the suspension by bracing with steel crossbars, but steel is in no way lightweight.
The upside of buying a high-end aluminum stroller is that they don't really lose value. You can almost always resell them on E-bay for nearly what you paid new.
