Re-negotiating Sales Price

[Preston Roth]

Hello Bigger Pockets family! I have a question. I'm currently in contract on a 36 unit complex and currently going through my investigative process. During my investigative work I have found that the insurance for the building is going to be 3 times what the current owner is paying as the current insurance company has changed underwriting rules and the old owner has had this company for years so they have been grandfathered in. Current cost for the owner is 4500 a year, which is really good to begin with, they have a 10k deductible and it isn't insured for the full rebuild costs, so that too explains the lower cost. The quotes I have received are about 13kannually , about $700 more a month,  numbers which of course I did not figure into my calculations when I made my offer. I believe I should/need to renegotiate, but have never needed to do something like this in that past. Any suggestions how I should approach and or reevaluate what that 700 per month would equate in a lower price? I figured a 30 year loan on 125k equates to about 700 a month, should I look at reducing the offer by that much? Any thoughts would be greatly appreciated. I have no agent this is seller to buyer deal. I have great rapport with the current owner, so just need some thoughts on whats fair.