Personally I would (and did) look at the economics of it in two ways:
1) the "start up" cost. i.e. construction of walls, floors, insulation. obviously this cost would be significantly greater by going the pole barn route, but by going with the basement you have a shop NOW (or at least pretty close to now). when i had to make this choice, i did not have the funds for this type of start up.
2) the "operating costs" mainly heat. With all do respect to the southerners here, many of you may not have experience with COLD winters. This can be a VERY important factor in the decision making process due to the sometimes volatile cost of heating. I was in the same boat as you 2 years ago and opted for the basement mainly for this reason. I'm already heating this space and otherwise it was just going to collect junk. In northern Maine we can go months without getting above zero...thus having to keep a shop comfortable with those temps is very costly.
and a 3rd point not relating to economics:
another reason the basement is good, wifey will bring down fresh baked cookies and hot cocoa since she doesn't need to bundle up and put on her galoshes.
if none of my arguments worked i would think at least #3 should!
Cheers,
NWB
EDIT:
as for the SF differences: there is a significant size difference, but if you have too much space, i feel you do too much walking... im at about 450 sf now but would be quite happy with only about another 3-400 max. that is all assuming my workflow and work load remains the similar with minimal growth.
Last edited by NICK BARBOZA; 09-11-2009 at 3:12 PM.
Reason: forgot to compare the SF.
"there is no such thing as a mistake in woodworking, only opportunities to re-assess the design"