Think I got a good Sub-to Deal

[Dan White]

Hi,

I ran across a motivated seller on a four-family in an up-and-coming area.  He purchased for 100k in 04' and has put around 50k into it since then.  Says he owes little on it.  Asking $150k and I think there is lots of room for rents to come up, creating more value.  I believe it could sell for 200-220k if I got the rents up.  He doesn't want to mess with the tenants' rents because they are friends' family members.  

I would prefer to wholesale this place, however I am only going to get one shot at it...as he does not want to be bringing multiple people through.  Therefore, my plan is to purchase, increase the rents, and sell asap.  I don't have the cash to buy it for 150k.  What are my options with Subject to?  How might I structure this?  

All the best, 

Dan W.