Hi, Patrick,
I'm the member formerly known as Kate Gardner; since I couldn't figure out how to dump that tag I just created a new account. (Could you e-mail me about this? --Thanks.)
Call me crazy (you won't be the first), but last fall when the growing season was over, I spent a week or so blending sand into my heavy clayey soil by hand, and when I say by hand, I mean that eventually I was kneading the stuff to get the sand integrated. I've got small beds (obviously) and only did one or two of those, but it'll be interesting to see how they behave this year.
Replacing the soil isn't really an option at the moment; there simply isn't the money. Maybe someday . . . . In the meantime, I intend to compost like crazy. If I do decide to buy soil, I think I'd build raised beds and put the good soil on top of the old, rather than have some hauled off.
--Kate