First Mobile Deal Help

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About 2.5 acres with 7 mobiles. 2 large storage buildings and room for 2-3 more lots but no extra hook ups. Septic, electric and well water. Landlord owns all mobiles. The existing homes are in bad shape and the area is not great but not horrible. Zero amenities. Really just a piece of land with some hook ups and trees in a relatively poor but big town about 30 minutes from my house. Owner is older with health issues, has kept poor records and willing to owner finance at 20% down, 8% for 10 years. I could obtain better terms via local bank. According to his hand written/iffy records he rents the 7 lots for about 3,000/month. 2 are currently vacant. Asking price is ~173k My plan would be to sell the mobiles asap. Maybe 5k a piece? Then charge lot rent of 200-300 per unit with possibility of adding lots. I'm touring property Friday. Considering offering around 120k. Plans to sell all homes for 20-30k total and then rent lots for around 2000/month. Thoughts? Any good rules of thumb or guidelines for developing a price for smallish mobile lots? Thanks!