My favorite "lightweight" and "cheap" and "good" tripod is the Bogen 3033, which is no longer made. It is not light compared to a carbon fiber tripod, but it is light in my book, considering the sturdiness and quality. IMO, it is the best balance of sturdiness, quickness, lightness, and cost. I would describe it as a "medium-format version of the 3036". Same basic construction, but lower capacity, and different ways of spreading and extending the legs. The 3033 is much quicker to set up, because all three legs spread at once, being connected to a sliding collar on the center of the tripod. It is also a bit quicker because the extension clamps are quick-action ones that only require a mild flip of a few degrees, while the 3036 camps are stiffer and require a full 90 degree flip. I find it far superior to the 3021 and 3030, which I do not like at all because the legs are not connected with struts to the center of the tripod. I can't stand this type of tripod design, myself.
As for weight, the first time I picked it up, it felt like a feather to me, being used to my 3051 and 3036. It seems that my definition of "light" tends to be different than most, however. Personally, I say that the 3033 is light enough to take hiking without "feeling it". (I hike the San Gabriel Mountains here in CA frequently, FWIW.) I have hauled my bigger tripods on hikes, but only short ones (a few miles tops), and I definitely "felt it", and did not feel agile enough to do the type of climbing I would normally do with the 3033.
I have used the 3033 for 4x5 cameras, and it worked just fine, though I would use a 3036 or 3051 if I didn't have to haul the thing long distances.
The head you choose will affect the weight and carrying comfort significantly. I suggest getting the legs with a standard 3047 head. This is a good head to have for general purposes, and the tripod will likely come with one at little additional cost on the used market. However, I would also go in to a shop and try different ones as well. There are others that are lower in profile and in weight, and will support an RB/RZ just fine.
I got my 3033 with a 3047 head for $60 in very clean condition. They are one of the best buys around, IMO.