Due to the few types of boots out there and the rarity of creatures dropping them they can be very expensive. Leather Boots can be found in great abundance, but anything (including Crocodile Boots) except sandals will cost a lot more. I.e. when the Tiquanda update came around in 2005 crocodile boots were priced at around 15k - and nowadays are sold for around 1k.
The strongest boots are the Golden Boots, but most people use Boots of Haste(BoH). A favorite method amongst high level knights is to carry Steel Boots around with them to slip on instead of Boots of Haste when they fight fierce monsters. Also, nowadays Soft Boots is also carried around as a good item for mana and health regeneration, mostly used by high levels.