I just moved in a couple to a two bedroom and moved another couple into a two-bedroom. 

They stated the current rents were at an average of $480, but the market rent was $650 for 1 bedroom units in this area.

It’s an old 2 bedroom with no basement and a functionally obsolete garage.

I'm looking for a 3-4 bedroom single unit, and I plan on living in one of the rooms so I will qualify for a FHA loan.

1) small room, furnished as bedroom + medium room unfurnished - long-term leases2) small room, furnished as bedroom, 30 day leases + medium room, unfurnished, long- term lease3) small room, unfurnished, marketed as a private office + medium room, unfurnished, marketed as bedroom - long-term lease4) small room, unfurnished, marketed as a private office + medium room, unfurnished, marketed as bedroom - 30 day leasesTYA!

We keep the comps on file by town and bedroom so we know where we stand.

My original idea was to buy a 6 bedroom house in marginal neighborhood for 75k with total around 25k.

If you see that several appraisals all estimate that an additional bedroom has a $15K value swing or a garage is $20k you can start honing in on some loose numbers.  

I live in a 1 bed room unit and rent out the 3 bedroom unit for $2400 a month what do you think a 3 bedroom and 1 bedroom unit could go for in 5-10 years ?

I do think large properties (5+ bedrooms) book more on Vrbo, but cannot back that up with anything more than anecdotal information.