Thanks guys for your replies!

We are looking at bidding $120,000 for foreclosure. Comps are considerably higher ($170k+) but it will need work. (Fortunately, mostly stuff I can do. We will need to put maybe $12k in, probably less)

Here is my math.
-Taxes are accurate.
-Repairs are a guess for an average year.
-Insurance is a guesstimate.
-I worked backwards from a mortgage calculator site, putting in home prices & interest rates and seeing the resulting mortgage payment.

House rents for $1200 a month AND assuming 10 months occupancy
$12000 - $3600 (tax) - $900 (repairs) - $1,000 (insurance)
$6500 left for mortgage ($6500/12 = $542/month)
= Can't pay more than $117,000

House rents for $1200 a month AND assuming 11 months occupancy
$13200 - $3600 (tax) - $900 (repairs) - $1,000 (insurance)
$7700 left for mortgage ($7700/12 = $642 month)
=Can't pay more than $142,000

To be honest, we are not planning to go any higher than $120k. But I just wondered about my numbers. Maybe (probably!) there is a lot I'm not seeing.

I really appreciate your feedback.

Molly