Before I get started, note that this price is for CRAFTABLE Ball-Kicking Boots, an item born from a temporary glitch that would remove the uncraftable status from items when traded. There aren't a lot and they're definitely a niche market. Uncraftable boots have a separate price on this site.

First two links: Ball-Kicking Boots that haven't traded hands yet. Offer of 1.5 buds in the most recent, claims of an offer of $70 in the older one (I can't verify it, but it looks like it fell through regardless since it's no longer noted in the most recent trade).

Third link has two noted current offers, one of a bit under two buds, one of 2 buds straight. The fellow who offered 42 keys now owns a pair, though through a trade I can't pinpoint and not from this fellow. It is unknown who was gathering two buds, though it is clear a trade WAS completed, as the new owner is the fellow with the final link.

Fourth link. Asking for 4 buds, but no actual offers just yet. I mainly include this as it's the only remaining clean boots trade around tf2outpost as of the time of this suggestion.

From the older trades, we can see offers of below and over two buds, though those over seem not to have gone through in the end. The most recent trade of this item seems to indicate it was sold for 2 buds straight. It's also worth noting that the partnering item, craftable Merc's Pride Scarfs, are all asking for 2 buds on outpost right now, which I would argue further supports this price.