Lens purchase help

I have the opportunity to purchase a near new 85.1.8 nikor lens from a work mate for $300 he has gone feral and ordered a Cannon D20 he also owns a new Volvo
. At present I have 50 1.8 70 210 + kit lens . My next lens was to be a 24 120 VR should I wait or go for 85 1.8 now and save again. DOSE LENS LUST EVER END IT"S WORSE THAN BEER AND DRUGS !!!!!!!!!!! . It is really great having this site to help me spend my hard earned cash THANK YOU all in advance LOZ : 


