With those prices it might be cheaper to reverse engineer regular Twitter API used by their web interface and Nitter.
Why wouldnt it be legal in this instance?
But later, eBay successfully sued Bidder's Edge to prevent them from spidering eBay's site:
https://en.wikipedia.org/wiki/EBay_v._Bidder%27s_Edge
Courts in later cases have disagreed with this ruling.
The bigger issue IMO is that it can get pretty hard to spider a site if they are actively trying to prevent you from doing it. It turns into a not-so-fun game of cat and mouse.