I'd like to be able to record an interviewee's vocals to a R-09 SD-card recorder carried in his jacket pocket. I'll sync it later on the NLE timeline.

The R-09 has "plug-in power" on its 3.5mm input jack - its spec sheet says this is 3Volts.

Any recommendation on a decent-sounding, modest- to medium-priced lavalier that could plug directly into the R-09 and run off its plug-in power?

Thanks.

I would recommend a giant squid lavalier.
You can't beat it for value.
http://www.giant-squid-audio-lab.com/gs/gs-mono1.htm

Thanks for the recommendation!