Me being a complete CRT newbie mysef, I can an only give you limited advice.
A line doubler is a device that you run video through and it doubles the lines of resolution going to the projector, they are necisary for CRTs since they have no onboard processing, these cost anywhere from 2k and up.
There is a cheaper solution. You can build a cheap HTPC(with an ATI Radeon card), and put a Holo3DGraph card in it, and run all the video though it, and to the pj via RGB. I'm doing this, however I'm adding a good soundcard and a DVD-rom drive as HTPCs with a Radeon video card produce the best image possible.
http://www.jvb.nl/jvb.asp?cur=2§...itle&title=116
About the Holo3DGraph, an even cheaper solution is to get a decent capture card(like Flyvideo 2000), and combine it with dscaler software(
http://www.dscaler.org/ ), and it will give you a simular picture to the Holo3DGraph card. Thing is, the capture card option is limited to S-video only, which isn't bad.
I'm hopefully about to get a Barco 801 with a little over 1,000hrs on it, for $1000 or under!