lighting filters

>Does anyone out there know
>where I can get a relatively cheap filter that lets mostly far red light
>(730) through?

I used to be involved with theatrical lighting, some of the gels that we
used to use would come close to that. The best way to find out would be
to contact Lee Lighting, or Rosco, or a store near you that sells gels for
theatrical use. They will have small sample books of gels, normally each 
separating page has the transmission spectrum for the accompanying 
filter, so all you will need to do is to look for a very deep red gel, and 
check what the specs for it are. 

Marque APD - ANGFA(NSW) <><