I kinda explained the pricing of this figure in the post immediately before yours...
Last one selling in the US on eBay was in the $200-250 range. Another seller tried two or three years later for around $400, but was unable to sell it, from what I understand. He may have sold it elsewhere, but I do not recall seeing it on ebay... and again, I'm a TM nut, so I do pay attention to this stuff. I feel stupid for not archiving those auctions, but I just wasn't thinking about it at the time.
EDIT: FOUND IT! Listed at $249.99 and closed at the end of April, 2008, though now that I see the auction, I don't think it sold. This may have been the one that went for $250 or was re-listed down from $400. I don't have any notes, and I only have the response from the seller. I gave him some information about the figure, but I just don't remember what it was!
EDIT 2: Pretty sure this was the first. I bought the second Biollante off Ruten in March of 2009. I remember seeing another Biollante on eBay after that, so the $400 one must have come later.
Now, if you're talking about the 6" Biollante, that tends to go for around $50-75 (crazy, I know). There have been a few sellers asking $100, but I don't think those sell very well.
Trendmasters prices have been very inflated the last few years. Still, I don't know how much demand there is for Biollante. If the last one and perhaps the one before didn't sell, who knows what you could get for her. The 10" Space G pushes $100 in some cases, but that's boxed. And usually it's when a glut of 10" figures show up. I used to think Biollante was the pinnacle of TM Godzilla collecting, but I may have been more alone in that than I thought considering the low demand. I guess with the Mega Mutations and Animated protos FINALLY hitting the web, a production phase 10" Biollante just doesn't cut it. Still don't see why. Despite the odd head, she's one of my favorites. I have her taking center place on the wall above my desk.
As to armored Anguirus, I'm after that and a boxed Kumonga.
Both made it out, and there was an Angy at G-Fest a few years back, but I have no idea what it sold for or if it did.
Actually, there was a very cool incident a few years back (EDIT: May of 2007
) where a guy in St Louis picked up both Angy and Kumonga for $2 or $3 each at a flea market! He asked the folks over at CT if they were rare and if he should let his son play with them. Of course, we told him how rare they were, but that he should let his son enjoy them. Pretty cool find, there.
Then the other Kumongas were bought up and sold on ebay for like $300 and then $250, I think? But that is the only thing I know about an Armored Anguirus outside of the CT photos. Heck, I don't think I've even seen prototypes... which is really annoying.
How much were the Kumongas going for at GFest? I've been looking for these two forever!