Probably the best option would be a Yongnuo 622TX and 2x YN622N, if these offer the same functionality as the Canon versions. I have the Canon Version which allows me to mix both ETTL and Manual flashes on separate Groups. If the Nikon versions allow the same, the Metz would be manual and the SB700 could be manual or ITTL. Perhaps somebody who has the Nikon Version could confirm if this is the case. Alternately, if everything is in manual mode, there are plenty of slightly cheaper options, such as the Youngnuo RF603's or such as the Commlite G430 series. I have the older version of the Commlites, the Ojecoco H430 series for Nikons and they work very well for off camera flash or to trigger Studio strobes.