Free and clear: Cash offer or seller fin.?

[Joe Butcher]

Heres the situation:

The house is owned free and clear

Seller is motivated but not desperate. It was listed on MLS and didn't sell.

ARV: $150k

Rehab est: 20k

My cash offer: 80k

I dont think they will accept the cash offer, so I want to offer a seller finance, just not quite sure what to offer so here is one scenario I came up with:

$135k with 5K down at 5% interest, amortized at 30 years with balloon due in 5 years.

Does that make sense? Does it sound reasonable? I am not totally familiar with seller financing so I may be way off here....feel free to tell me I'm crazy or whatever. If it's not an attractive offer, then what is?

Joe Butcher