It looks like we can do the electronic registration (which is significantly cheaper than the form-and-check-by-mail option). We'll still have to mail them hard copies of the Actual Books (and I need to find how many of each book has to be submitted; it used to be...three?), but the cost to register is around $35/book (ref: http://www.copyright.gov/eco/ and http://www.copyright.gov/eco/faq.html)

So, that's seven or ten books (haven't figured out if the two omnibi are two books or five) @$35 + postage. Five hundred bucks, say, worst case, when the smoke clears. And, as Steve points out, the time off from writing and the aggravation and the wondering what the HELL the Authors Guild was thinking...