RF Radio Modules
Here is a summary of sources of radio modules and some suggestions on models that I found interesting. I have been using the SILRX / TXM radios from from RadioMetrix to date but they are getting a little long in the tooth.
Linx - mfr. of radio modules, distributed by Digikey
*** Low cost modules look good but are SMD only - $7/$14.
*** The TR-916-SC tranceiver looks interesting - 33.6Kbps, $45 ea
Lemos International - no pricing on website - geared to OEM
Abacom - wide range of modules
*** ATRT100-xxx $57 for tranceiver, 100 Kbps, FM
*** RTL-Data-SAW $17 for tranceiver, 4800 bps, AM
*** AM-RT4 / AM-HRR3 xmtr/rcvr $12/$11, 2400 bps, AM
*** FMRTF3 / FMRRF1 xmtr/rcvr FM - $12/$25, 9600 bps
Mounts the Linx LC modules on a small board with pins for $14/$21, 4800 bps
*** Have inexpensive AM 2400 bps $8.50/$8.50 - best bet for low cost link.
RadioMetrix makes many of the modules sold by the above distributors and has
some good documentation