I heard that some people were running battery powered XLR mics directly into 3.5mm jack equipped camcorders and cameras with line matching transformers - so I set out on a quest to see if could make it work - and I did.
I'm now running a $75 used Audio Technica AT835 mic (sourced from eBay) directly into my GH2 with a $15 Hosa Low Z to High Z transformer and a $5 Hosa GPM-467 3.5mm to 2.5mm adapter. The windscreen is a $55 Olsen Mic Muff MM-21. It works really well for my application (standups right in front of the camera for my vlog).
The preamps on the GH2 are not great, but they are good enough for this - and the GH3's are even better.
No phantom power - but that's what battery powered mics are for.
When this setup is connected to the GH3, I won't need the GPM-467 any more. A lot less expensive than Panasonic's $349 OEM solution :)