I've got the Samson Airline Am1/Ax1 wireless on camera mic system, but now i need a lav mic to plug into the transmitter. Therefore i need to find a decent omnidirectional lavalier (that is also cost effective!) with XLR connector that takes batts or doesn't need power - any suggestions!?

Does anyone know of ANY lavs with XLR output???

There are several lavs available with XLR output that can use an internal battery and connect with your XLR plug-on transmitter.
The one I normally recommend has a cable length from the lav element to the battery/XLR housing that would probably be very inconvenient with a plug-on transmitter. Basically this will be true of many lavs designed for wired use.
The AT899 omni lav is very good and costs $200. Like I said, the extra long micro cable (10 feet) is handy for wired use, but you'll have to deal with it somehow when using the plug-on.
There are other models from AT and Sony that can run on internal battery power and have shorter cables between the lav and the battery/XLR housing.
There's also the Shure SM11 dynamic lav, although it's huge and dull-sounding. It would be convenient, but I wouldn't recommend it due to its size and sound.