Scott, for best DVD performance get a good progressive-scan DVD player like the Panasonic RP-82. The quality of the deinterlacing in that unit is usually superior to an external line doubler, at least the affordable ones.
Use an affordable line-doubler like the IScan for your non-DVD sources. Your projector will have its own deinterlacer built in, so you could get away without a line-doubler at all if the quality of television and other video sources doesn't matter to you much. If it does matter, get the IScan.
The cost of the RP-82 and an IScan v2 will run you about $600 together, which is pretty reasonable for front projection needs, and then you will have the best of both worlds.