Ex Officio Amphi Pants are great for warm weather hiking. You can get them in full-length, convertible, or as shorts. Gramicci makes a Quick Dry version of their climbing pants. Neither will be a huge weight savings over the Sahara pants, but you may shave a few ounces.
Remember to make apples-and-apples comparisons. Most running shorts have built-in briefs so there is a couple ounce offset right away. Most of the hiking pants have belts that add a few ounces.
I've picked up several pairs of running pants in thrift stores by companies like Hind and New Balance, but most are black and so are not very suitable for hiking exposed sunny trails. They hover around the 6oz mark. They are great for cool-weather cover up and at $5 or so a pair they can be sacrificial-- if I give them a beating, I'm not out much.
I've gone through the same problem myself and it seems to break down like this for me to get UL with pants:
Wear running shorts. You can find all kinds with briefs built in. I find them in thrift stores and garage sales for $2-$5 a pair for name brands like New Balance and Nike. Benefits: low cost, light weight, low chafe, quick dry. Caveats: no sun or bug protection. Wear sun screen and add a pair of UL wind pants like Mont-Bell, Montane, or GoLite-- or rely on your rain pants to fill that niche. The running short and wind/rain pant combo seems to be the choice of most long-distance hikers. It does seem to provide the most adapability for the weight. Running shorts with briefs aren't much more weight than briefs alone so the question is: can you tolerate the exposure to sun and bugs?
Wear convertibles and live with the extra weight offset by the multi-use factor. Most are more durable than running gear and wind pants. I don't mind a little extra weight for pants as they take the real beating from brush, mud, rocks, sitting, etc. I'd love to have a pair of Mont-Bell wind pants (2.5oz), but the idea of sitting in mud/dirt/gravel/sticks in a $70 pair of paper thin pants doesn't sound so hot.
I would like a pair of hiking pants that are light weight and light colored, fairly wind-resistant and water repellent (still breathable), with a minimum of pockets and other trappings, belt loops (but not a captive belt), available in several inseam lengths, and a button and loop arrangment so they can be rolled up to just below the knee. Add a waist with a light microfleece lining and conical build like Mountain Hardwear's.