I can think of a number of ways to accomplish this, but see no need to reinvent the wheel. We are working on updating several areas of our building. Our pastor wants to add video screens for announcements/info. I am assuming something along the lines of a looping powerpoint/keynote presentation. At some point we may want to send live service video to them as well. What is the best way (that obviously depends-I'm looking for reasonable cost and flexibility/expandability) to distribute the video display? Given our building most runs will be 150 feet or less of cable-should not see anything over 300 feet ever.
Couple of options, depending on how you want to do it. Cabling-wise, Coax (RG6) cable is cheapest; connect your source to an RF Modulator (ZeeVee, for example) to convert your signal to a digital channel, and tune the TV's to that. Eliminates the need for conversion boxes at each display. Also opens up the possibility of multiple channels.
Next step up would be to add Digital Signage boxes as the source for the looping display. This would allow you to have different loops at different locations. When you need to go live, change the source on the TV to the cable input. This would require network run to every TV as well (though you should do this anyway).
Step up from that would be to get Digital Signage boxes with built-in QAM tuners. This would allow you to have a signage loop, with an embedded live display. This could be timed to change to live feed using the built-in clocks, eliminating the need for human intervention (and its inherent forgetfulness). The signage boxes also have the advantage of turning the TV's on and off as needed, based on the clock.
Alternatively, to achieve option 3, you could skip the modulator and get Digital Signage boxes that will accept an H.264 stream. You'd then need a converter that will embed your live feed into an H.264 stream.
With the variety of options as outlined above available now, I'd steer away from HDSDI distribution with a network of four or more TV's. Too limiting.