Land and New Construction financing

[Raphael Cuthbertson]

Hi folks, 

Got an opportunity to pick up 5 lots in existing neighborhoods from same seller.  Seller has been building houses but will be returning to Medical School in July of 2016.  ALL TAP FEES ARE PAID.

He will give me a juicy discount on the land if I buy all five, and a lesser discount for picking single properties.

What I want to do is buy them, and build houses one at a time.  But first, I need to find out how much to pay.  I had a newish real estate agent run comps in the neighborhoods. I see the surrounding house comps ($130k - 179k range for AVM), but cannot determine from the comps what the raw land is worth, save for the meaningless county assessment.

I was told by the seller (a broker himself) that the general rule is 25% of what the new house would sell for.  On the other hand, a long time investor told me that I should be looking at $25 of the cost to build (figuring a 2100-1300 sq foot home at around $35/sq ft).  Which rule do you use?  

On top of all that, I'm not necessarily penniless, but do not have the capital to buy the lots, let alone build homes.  I understand that land is hard to find private money for, but I still would prefer to develop these lots rather than wholesaling them.  I keep asking myself "what's in it for an investor in the land?".  How do I get investment money on 5 lots, then turn around and get investment money on the builds too?