'09 - I wouldn't go any higher than $2000 below invoice
'10 - I wouldn't go any higher than $500 below invoice
With that being said, that is the max price and you have a lot of factors going for you (time and money). I think you should go for these deals:
'09 - $2500 - $3000 below invoice
'10 - $1500 below invoice
2009 / 2010 Nissan 370z invoice Price