As to lumens, the brighter the pj, the typically earlier to watch- maybe 20-30 minutes depending on the weather/time of dusk. I would also consider as good a resolution as you can get- a 1024x768 XGA pj = 576p only for 16:9/movie material so this would be the bare minimum for projection.
I was able to purchase a Benq PE7700 DLP HD 16:9 with full factory warranty directly from the factory (REFURB) last year for $800. It's a notable improvement over my 4:3 XGA Benq PB6200. Either of my PJ's will project fine to any screen size I have seen here. I'm running 8 x 16 feet in the backyard with no problems. Could go bigger.
This ain't no upwardly mobile freeway, this is the road to hell.