My Epson is a "lowly" 2k lumens, and came in under 500 bucks, and it does me just fine.
If I was doing VDJ or something else requiring extended periods of projection for professionally produced material, of course more brightness and better specs would be in order, but for the occasional client-produced slideshow or video-montage, it suits me just fine, and anything else would be overkill.
If I had to do my initial purchase over again, or when I start to upgrade down the road, I would move to a rear-projection screen.
And Scott is right about venue pricing for video rentals... one venue in particular here will charge you $200 for projector and screen rental, and for that price they just throw it in a pile in the corner of the room! You provide laptop, hook it up, run it, etc.
Against that, my $99 projection add-on is a steal! Plus I have the benefit of knowing what to expect and what to do - not wondering if their stuff will end up working... Because even if you and the client know that venue-provided or client-rented equipment malfunction or idiosyncrasy isn't your responsibility or fault, such will reflect negatively upon you for all present whilst you scramble about trying to figure out why S ain't workin!