tell me what you think of this way to look at buying a farm.....

for arguments sake we will use some numbers here
20 acres total.
18.5 tillable
$7000 an acre/$140,000 total price
or $7560 a tillable acre.
155 bushel corn
 corn $5.00
cost $500 an acre to put out a crop (seed chem fert mach fuel cropins)

put $50,000 down on farm and finance $90,000

my first question of many is..... if i finance it for say 4% for 30 years then the first years interest will be $194 a tillable acre.... which is reasonable rent for this area. if i can make $280 after paying seed/chem/fert/mach/crop ins. then i'm making $86 an acre before paying principal and property taxes (probably $15/a for prop tax) if i'm only making $1500 off the farm then i'm getting a 3% return on my money in equity (principal payments) correct? which will go up as i pay more of the principal off and the interest portion is lower over time...... does anyone look at it this way?

I'm just trying to justify buying another 20 ac at what i consider is a high price. ($7000 an acre for this particular piece). i know there thinking someone will buy it to build a house on, but it is within 2 miles of the house/20 acres i'm buying now so thought it might be a good close addition... i'm so confused on if i should just wait out this market or if we are only in the beginnings of a boom.

i used to be in the bust is right around the corner camp... but i think my impatientness is gettint the best of me!

am i being too conservative/or do i expect too much return for my money?

fire away fellas! nothing is too rude or forward at this point!