TigerDirect offers the H&R Block At Home Deluxe Federal + State 2011 for Windows and Mac, model no. 1336600-11, for $44.99. Coupon code "QYF55684" cuts it to $19.99. With $4.79 for shipping, that's the lowest total price we could find by $7 (outside of the deal below), although we saw it for $3 less two weeks ago. This software is intended for homeowners and investors.
Of note, Amazon has it for $24.99 with free shipping for its Amazon Prime members.