navizon keeps the gps going, it has an autostart, and it's own power management. it's free, and can make you some $ (if you want to have it tethered to a power source for wifi)
but seriously, if you have the wifi off, you will only typical drain associated with the device not being in full standby and gps radio on.
also an interesting thing i've noticed is that sometimes if I have my wifi off and go into a bigbox store (depot/wallyworld) I have to reset to get gps lock again.....
BUT if I have my wifi ON (running navizon) and there are wifi signals (~45 AP's in the store i was in tonight.), I get my lock back when i leave.