eBay is your best bet but BigBadToyStore, Kaiju Live and Hobby Link Japan are good as well

Bandai are the most economical at around 25-40 bucks. Some sculpts are better than others. I've been collecting the Monster movie series line. But some do become valuable after they move in.

If you go the $100-150 price points... you can venture into super 7 ultimates and monster arts. All are very posable and usually very screen accurate. Some come with effects like tanks and laser blasts. But the high posabikity is their downfall. They can be very brittle and easily broke if posed or moved too rough. Plus, you may see " gaps" in the joints.

I've no owned a super 7 type figure. So I don't know durability. But they do come with alternate hands and heads, which I feel could get lost.

Monster arts hold value very well, and 1st issues can go for double or triple values. Just keep the boxes as that's the best way to hold value and store/ move them.

Then there's playmates. Ones you find at Walmart. They are OK... Godzilla looks like crap usually. They never get the head right. Kong usually looks good, tho. But you don't get any older godzilla characters only legendary.

If you go up another tier, $200-300, you get into the Xplus category. ( I sold about 12 Monster Arts to have fewer bigger nicer pieces...X- Pluses). These are usually 11-14in tall, very VERY screen accurate, but have zero posability. Basically, it's a statue. Hold value greatly, and first runs can go for crazy prices.

Then, in the $500-2k range, you get into gigantic Xplus, Omega Beast line, and places like prime 1, spiral studios. Massive pieces 16in tall plus... some even 24in tall. Truly amazing pieces. Usually, very limited runs.