Sunfire Load Invarient 2 channel amp 2 x 300

Can anyone tell me the current Blue Book price and / or last sold prices for 1 of these amps? There are a couple on eBay I am looking at and want to make a realistic offer to purchase. I have 1 now looking for another to vertically bi-amp to my Appogee Centaur Majors running through a cj pv12-al pre that I got here at the a'gon. (fantastic piece!) Is it worth the $'s for improved performance? I have read a few threads on doing this with the sig series, but none on the original 300W version.

Thanks!