@Barrett Frische
Destroy All Monsters, both the ADV and Media Blasters versions, are out of print and very hard to find. The ADV version has been out of print for over 10 years and the Media Blasters version was halted by Toho for having special features that they didn't approve. So you're only going to find them for very expensive prices. Your best bet is eBay or keep looking for a used copy that is in your price range.
The good news is Media Blasters has (apparently) resolved their issues with Toho, so there's a chance they may re-release Destroy All Monsters in the future.
@Shrek
Godzilla vs. the Sea Monster, Son of Godzilla, Godzilla vs. Hedorah, Godzilla vs. Gigan and Godzilla vs. MechaGodzilla are also out of print. Sony used to own the DVD rights to them, but decided to let them go. Now Toho has the rights back and some other American company will have to negociate with Toho if we ever want to see a re-release of those movies again.
Godzilla 1985 has some complicated rights issues that most people refer to as a black hole. An official DVD of the movie has never been released and it seems unlikely it will be released anytime soon.
"'Nostalgic' does not equal 'good,' and 'standards' does not equal 'elitism.'" "Being offended is inevitable. Living offended is your choice."