re: What is a reasonable price to pay for tax filing preparation?

I just filed for an extension. Turbo Tax said I owed $6K in federal and $1K in state taxes. I think when my wife started working last year, we didn't file her W4 properly. I paid the state tax and mailed a check for $2K along with Form 4868. I need some sometime to regroup and see if we can find more deductions.

This is the first time I have underpaid my taxes. Do you think the IRS will penalize me for under payment or something?