@Tim HockerI agree with the comments saying you need a bigger cash cushion.

Agree with Charlie on short term in Boston - new regs make that less feasible in Boston proper - but I work with folks who have robust portfolios of short term rentals in Malden and Chelsea, with the transit access of Boston but fewer limitations.

He agreed but since he was busy on the job we didn't really have time to discuss it further.So of course, one option would be for me to just be his private money guy and structure it as a debt deal, but I'd really rather get a little more skin in the game and partner with him. 

I would agree with @Karen Rittenhouse and recommend you speak with a local attorney @Austin McKellar.

@Dennis M.I agree, but I think there is room to negotiate, but I am not sure how to approach it without offending him or cutting off negotiations. 

I pretty much agree with @Omar Khan.You can do both.

I would agree with Jessicas' assessment and advice of the differences between the two counties @Etahn Smith keep searching Bergen County there are good deals to be had there, as you do your research you may even stumble upon a few areas where deals exist that are currently flying under the radar ;-)

SO they can agree to payments and maybe a premium. 

You all agreed on X, Y, Z done by your guy for $230. 

I agree as well with @Jay Hinrichs If possible--- owner finance the deal as well to earn some trailing $--- 20% down and some cash over time is great.