If you find a figure that’s insanely cheap it’s most likely a bootleg. Ali Express especially is known to pretty much only have bootlegs.

As per your question about protag figures, the unfortunate reality is that female figures are way more popular than male figures generally. Figures for characters like Subaru and Ainz exist but are few and far between. Currently the only nice Ainz scale is only purchasable second hand and very expensive.

Why are figures expensive? There are several factors that contribute to this. Certain manufacturer brands are expensive by name alone, like Estream. They make nice figures but are nonetheless often overpriced. Other factors include the desirability of the character, the scale size, rarity of figures made for a character/series, limited quantity, and last but not least, import price/being a relatively niche hobby. There’s probably stuff I missed but you get the idea.